SlideShare a Scribd company logo
5
Most read
6
Most read
7
Most read
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 1
Unit-II: GAMMA, BETA FUNCTION
Sr. No. Name of the Topic Page No.
1 Definition of Gamma function 2
2 Examples Based on Gamma Function 3
3 Beta function 5
4 Relation between Beta and Gamma Functions 5
5 Dirichlet’s Integral 9
6 Application to Area & Volume: Liouville’s
extension of dirichlet theorem
11
7 Reference Book 13
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 2
GAMMA, BETA FUNCTION
 The Gamma function and Beta functions belong to the category of the
special transcendental functions and are defined in terms of improper
definite integrals.
1.1 Definition of Gamma function :
The gamma function is denoted and defined by the integral
Γ𝑚 = ∫ 𝑒−𝑥
𝑥 𝑚−1
𝑑𝑥 (𝑚 > 0)
∞
0
1.2 Properties of Gamma function :
1) Γ( 𝑚 + 1) = 𝑚Γ𝑚
2) Γ( 𝑚 + 1) = 𝑚! When m is a positive integer.
3) Γ( 𝑚 + 𝑎) = ( 𝑚 + 𝑎 − 1)( 𝑚 + 𝑎 − 2)……… 𝑎Γ𝑎, when n is a
positive integer.
4) Γ𝑚 = 2 ∫ 𝑒−𝑥2
𝑥2𝑚−1
𝑑𝑥 ( 𝑚 > 0)
∞
0
5)
Γ𝑚
𝑡 𝑚
= ∫ 𝑒−𝑡𝑥
𝑥 𝑚−1
𝑑𝑥 ( 𝑚 > 0)
∞
0
6) Γ
1
2
= √ 𝜋
7) ∫ 𝑒−𝑥2
𝑑𝑥 =
√𝜋
2
∞
0
8) ∫ 𝑥 𝑛
(𝑙𝑜𝑔 𝑥) 𝑚
𝑑𝑥 =
(−1) 𝑚
( 𝑛+1) 𝑚+1
Γ(𝑚 + 1)
1
0
2.1 Examples Based on Gamma Function:
Example 1: Evaluate 𝚪(−
𝟏
𝟐
).
Solution: We know that Γ( 𝑚 + 1) = 𝑚Γ𝑚
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 3
 Γ (−
1
2
+ 1) = −
1
2
Γ (−
1
2
)
 Γ (
1
2
) = −
1
2
Γ(−
1
2
)
 √ 𝜋 = −
1
2
Γ (−
1
2
)
∴ 𝚪(−
𝟏
𝟐
) = −𝟐√ 𝝅. __________Ans.
Example 2: Evaluate ∫ √ 𝒙𝟒
𝒆−√𝒙
𝒅𝒙
∞
𝟎
Solution: Let 𝐼 = ∫ 𝑥
1
4 𝑒−√𝑥
𝑑𝑥
∞
0
__________(i)
Putting √ 𝑥 = 𝑡 ⟹ 𝑥 = 𝑡2
so that 𝑑𝑥 = 2𝑡 in (i), we get
𝐼 = ∫ 𝑡1 2⁄
𝑒−𝑡
2𝑡 𝑑𝑡
∞
0
= 2∫ 𝑡3 2⁄
𝑒−𝑡
𝑑𝑡
∞
0
= 2∫ 𝑡
5
2
−1
𝑒−𝑡
𝑑𝑡
∞
0
= 2Γ(
5
2
)
= (2 ×
3
2
)Γ (
3
2
)
= (2 ×
3
2
×
1
2
)Γ (
1
2
)
=
3
2
√ 𝜋
∴ ∫ √ 𝒙𝟒
𝒆−√𝒙
𝒅𝒙
∞
𝟎
=
𝟑
𝟐
√ 𝝅 ________Ans.
Example 3: Evaluate ∫
𝒙 𝒂
𝒂 𝒙
𝒅𝒙
∞
𝟎
.
Solution: Let 𝐼 = ∫
𝑥 𝑎
𝑎 𝑥
𝑑𝑥
∞
0
_______ (i)
Putting 𝑎 𝑥
= 𝑒 𝑡
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 4
⟹ 𝑥 log 𝑎 = 𝑡
⟹ 𝑥 =
1
log 𝑎
⟹ 𝑑𝑥 =
𝑑𝑡
log 𝑎
in (i), we have
𝐼 = ∫ (
𝑡
log 𝑎
)
𝑎
𝑒−𝑡∞
0
𝑑𝑡
log 𝑎
=
1
(log 𝑎) 𝑎+1 ∫ 𝑒−𝑡
𝑡 𝑎
𝑑𝑡
∞
0
=
1
(log 𝑎) 𝑎+1 ∫ 𝑡( 𝑎+1)−1
𝑒−𝑡
𝑑𝑡
∞
0
=
1
(log 𝑎) 𝑎+1
Γ(𝑎 + 1)
∴ ∫
𝒙 𝒂
𝒂 𝒙
𝒅𝒙
∞
𝟎
=
𝟏
( 𝐥𝐨𝐠 𝒂) 𝒂+𝟏
𝚪(𝒂 + 𝟏) ________ Ans.
Example 4: Prove that ∫ ( 𝒙 𝒍𝒐𝒈𝒙) 𝟒
𝒅𝒙 =
𝟒!
𝟓 𝟓
𝟏
𝟎
Solution: We know that
∫ 𝑥 𝑛
(𝑙𝑜𝑔 𝑥) 𝑚
𝑑𝑥 =
(−1) 𝑚
( 𝑛+1) 𝑚+1
Γ(𝑚 + 1)
1
0
_______(i)
Now, ∫ ( 𝑥 𝑙𝑜𝑔𝑥)4
𝑑𝑥 =
1
0
∫ 𝑥41
0
( 𝑙𝑜𝑔𝑥)4
𝑑𝑥
Putting 𝑛 = 𝑚 = 4 in (i), we get
∫ 𝑥4
1
0
( 𝑙𝑜𝑔𝑥)4
𝑑𝑥 =
(−1)4
(4 + 1)4+1
Γ(4 + 1)
=
Γ5
55
=
4!
55
__________ proved.
2.2 EXERCISE:
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 5
1) Evaluate: (a) Γ(−
3
2
) (b) Γ (
7
2
) (c)Γ(0)
2) ∫ 𝑒−ℎ2 𝑥2
𝑑𝑥
∞
0
3) ∫
𝑑𝑥
√−𝑙𝑜𝑔𝑥
1
0
4) ∫ ( 𝑥 𝑙𝑜𝑔𝑥)3
𝑑𝑥
1
0
3.1 BETA FUNCTION:
Definition: The Beta function denoted by 𝛽( 𝑚, 𝑛) or 𝐵(𝑚, 𝑛) is defined as
𝐵( 𝑚, 𝑛) = ∫ 𝑥 𝑚−1
(1 − 𝑥) 𝑛−1
𝑑𝑥, (𝑚 > 0, 𝑛 > 0)
1
0
3.2 Properties of Beta function:
1) B(m,n)= B(n,m)
2) 𝐵( 𝑚, 𝑛) = 2 ∫ 𝑠𝑖𝑛2𝑚−1
𝜃 𝑐𝑜𝑠2𝑛−1
𝜃 𝑑𝜃
𝜋
2⁄
0
3) 𝐵( 𝑚, 𝑛) = ∫
𝑥 𝑚−1
(1+𝑥) 𝑚+𝑛
𝑑𝑥
∞
0
4) 𝐵( 𝑚, 𝑛) = ∫
𝑥 𝑚−1+𝑥 𝑛−1
(1+𝑥) 𝑚+𝑛
𝑑𝑥
1
0
4.1 RelationbetweenBeta and Gamma Functions:
Relation between Beta and gamma functions is
𝛽( 𝑚, 𝑛) =
Γm .Γn
Γ(m+n)
 Using above relation we can derive following results:
 ∫ 𝑠𝑖𝑛 𝑝
𝜃 𝑐𝑜𝑠 𝑝
𝜃 𝑑𝜃 =
1
2
𝛽 (
𝑝+1
2
,
𝑞+1
2
) =
Γ(
𝑝+1
2
).(
𝑞+1
2
)
2Γ(
𝑝+𝑞+2
2
)
𝜋
2⁄
0
 Γ (
1
2
) = √ 𝜋
 Euler’s formula:
Γ𝑛 . Γ(1 − 𝑛) =
𝜋
sin 𝑛𝜋
 Duplication formula:
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 6
Γ𝑛 . Γ(𝑛 +
1
2
) =
√𝜋 Γ(2𝑛)
22𝑛−1
4.2 EXAMPLES:
Example 1: Evaluate ∫ 𝒙 𝟒
(𝟏− √ 𝒙)
𝟓
𝒅𝒙
𝟏
𝟎
Solution: Let √ 𝑥 = 𝑡 ⟹ 𝑥 = 𝑡2
so that 𝑑𝑥 = 2𝑡 𝑑𝑡
∫ 𝑥4
(1− √ 𝑥)
5
𝑑𝑥 =
1
0
∫( 𝑡2)4 (1 − 𝑡)5
(2𝑡 𝑑𝑡)
1
0
= 2 ∫ 𝑡9
(1 − 𝑡)5
𝑑𝑡
1
0
= 2 𝐵(10,6)
= 2
Γ10 Γ6
Γ16
= 2 ×
9!5!
15!
=
2×1×2×3×4×5
15×14×13×12×11×10
=
1
11×13×7×15
=
1
15015
∴ ∫ 𝑥4
(1 − √ 𝑥)
5
𝑑𝑥 =
1
0
1
15015
_________ Ans.
Example 2: Find the value of 𝚪 (
𝟏
𝟐
).
Solution: We know that,
∫ 𝑠𝑖𝑛 𝑝
𝜃 𝑐𝑜𝑠 𝑝
𝜃 𝑑𝜃 =
Γ(
𝑝+1
2
).(
𝑞+1
2
)
2Γ(
𝑝+𝑞+2
2
)
𝜋
2⁄
0
Putting 𝑝 = 𝑞 = 0, we get ∫ 𝑑𝜃 =
𝚪(
𝟏
𝟐
) 𝚪(
𝟏
𝟐
)
2 𝚪𝟏
𝜋
2
0
 [ 𝜃]0
𝜋 2⁄
=
1
2
(Γ
1
2
)
2
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 7

𝜋
2
=
1
2
(Γ
1
2
)
2
 (Γ
1
2
)
2
= 𝜋
 Γ (
1
2
) = √ 𝜋 _______Ans.
Example 3: show that ∫ √ 𝒄𝒐𝒕𝜽 𝒅𝜽 =
𝟏
𝟐
𝚪(
𝟏
𝟒
) 𝚪 (
𝟑
𝟒
)
𝝅
𝟐
𝟎
Solution: We know that,
∫ 𝑠𝑖𝑛 𝑝
𝜃 𝑐𝑜𝑠 𝑝
𝜃 𝑑𝜃 =
Γ(
𝑝+1
2
).(
𝑞+1
2
)
2Γ(
𝑝+𝑞+2
2
)
𝜋
2⁄
0
∫ √ 𝑐𝑜𝑡𝜃𝑑𝜃 = ∫
𝑐𝑜𝑠1 2⁄
𝜃
𝑠𝑖𝑛1 2⁄ 𝜃
𝑑𝜃
𝜋
2
0
𝜋
2
0
= ∫ 𝑠𝑖𝑛−1 2⁄
𝜃
𝜋
2
0
𝑐𝑜𝑠1 2⁄
𝜃 𝑑𝜃
On applying formula (1), we have
∫ √ 𝑐𝑜𝑡𝜃𝑑𝜃 =
Γ(
−
1
2
+1
2
) Γ(
1
2
+1
2
)
2Γ(
−
1
2
+
1
2
+2
2
)
𝜋
2
0
=
Γ(
1
4
) Γ(
3
4
)
2 Γ(1)
=
1
2
Γ (
1
4
)Γ (
3
4
)
∴ ∫ √ 𝑐𝑜𝑡𝜃 𝑑𝜃 =
1
2
Γ (
1
4
)Γ (
3
4
)
𝜋
2
0
__________Ans.
Example 4: Evaluate ∫ ( 𝟏 + 𝒙) 𝒑−𝟏 ( 𝟏 − 𝒙) 𝒒−𝟏
𝒅𝒙
+𝟏
−𝟏
Solution: Put 𝑥 = 2cos 2𝜃, then 𝑑𝑥 = −2sin 2𝜃 𝑑𝜃 in
∫ (1 + 𝑥) 𝑝−1 (1 − 𝑥) 𝑞−1
𝑑𝑥
+1
−1
= ∫ (1 + 𝑐𝑜𝑠2𝜃) 𝑝−1(1 − 𝑐𝑜𝑠2𝜃) 𝑞−1(−2𝑠𝑖𝑛2𝜃)
0
𝜋
2
= ∫ (1 + 2𝑐𝑜𝑠2
𝜃 − 1) 𝑝−1(1 − 1 + 2𝑠𝑖𝑛2
𝜃) 𝑞−1(−4𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃 𝑑𝜃)
0
𝜋
2
= 4∫ 2 𝑝−1
𝑐𝑜𝑠2𝑝−2
𝜃 . 2 𝑞−1
𝑠𝑖𝑛2𝑞−2
𝜃 . 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜃 𝑑𝜃
𝜋
2
0
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 8
= 2 𝑝+𝑞
∫ 𝑠𝑖𝑛2𝑞−1
𝜃 𝑐𝑜𝑠2𝑝−1
𝜃
∞
0
𝑑𝜃
= 2 𝑝+𝑞
Γ(
2𝑞
2
) Γ(
2𝑝
2
)
2Γ(
2𝑝+2𝑞
2
)
= 2 𝑝+𝑞−1 Γ( 𝑝) Γ( 𝑞)
Γ( 𝑝+𝑞)
__________Ans.
Example 5: Show that 𝚪( 𝒏) 𝚪( 𝟏− 𝒏) =
𝝅
𝒔𝒊𝒏 𝒏𝝅
(𝟎 < 𝑛 < 1)
Solution: We know that
𝛽( 𝑚, 𝑛) = ∫
𝑥 𝑛−1
(1 + 𝑥) 𝑚+𝑛
𝑑𝑥
∞
0
Γ𝑚 Γ𝑛
Γ(𝑚+𝑛)
= ∫
𝑥 𝑛−1
(1+𝑥) 𝑚+𝑛
𝑑𝑥
∞
0
Putting 𝑚 + 𝑛 = 1 𝑜𝑟 𝑚 = 1 − 𝑛, we get
Γ(1−𝑛) Γ𝑛
Γ1
= ∫
𝑥 𝑛−1
(1+𝑥)1
𝑑𝑥
∞
0
Γ(1 − 𝑛)Γ𝑛 = ∫
𝑥 𝑛−1
1+𝑥
𝑑𝑥
∞
0
[∵ ∫
𝑥 𝑛−1
1+𝑥
𝑑𝑥
∞
0
=
𝜋
𝑠𝑖𝑛 𝑛𝜋
]
∴ Γ( 𝑛)Γ(1− 𝑛) =
𝜋
𝑠𝑖𝑛 𝑛𝜋
______proved.
4.3 EXERCISE:
1) Evaluate ∫ (1 − 𝑥3)−1 2⁄
𝑑𝑥
1
0
2) Evaluate ∫
𝑥 𝑚−1+𝑥 𝑛−1
(1+𝑥) 𝑚+𝑛
𝑑𝑥
1
0
3) Evaluate ∫ (
𝑥3
1−𝑥3
)
1
2
𝑑𝑥
1
0
4) Prove that Γ (
1
4
) Γ (
3
4
) = 𝜋√2
5) Show that 𝛽( 𝑝, 𝑞) = 𝛽( 𝑝 + 1, 𝑞) + (𝑝, 𝑞 + 1)
5.1 DIRICHLET’S INTEGRAL:
If 𝑙, 𝑚, 𝑛 are all positive, then the triple integral
∭ 𝑥 𝑙−1
𝑦 𝑚−1
𝑧 𝑛−1
𝑑𝑥 𝑑𝑦 𝑑𝑧
𝑉
=
Γ(l)Γ(m)Γ(n)
Γ(𝑙 + 𝑚 + 𝑛 + 1)
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 9
Where V is the region 𝑥 ≥ 0, 𝑦 ≥ 0, 𝑧 ≥ 0 and 𝑥 + 𝑦 + 𝑧 ≤ 1.
Note:
∭ 𝑥 𝑙−1
𝑦 𝑚−1
𝑧 𝑛−1
𝑑𝑥 𝑑𝑦 𝑑𝑧𝑉
=
Γ(l)Γ(m)Γ(n)
Γ(𝑙+𝑚+𝑛+1)
ℎ𝑙+𝑚+𝑛
Where V is the domain, 𝑥 ≥ 0, 𝑦 ≥ 0, 𝑧 ≥ 0 and 𝑥 + 𝑦 + 𝑧 ≤ ℎ
5.2 Corollary: Dirichlet’s theorem for n variables, the theorem status that
∭…∫ 𝑥1
𝑙1−1
𝑥2
𝑙2−1
… 𝑥 𝑛
𝑙 𝑛−1
𝑑𝑥1 𝑑𝑥2 𝑑𝑥3 … 𝑑𝑥 𝑛
=
Γ𝑙1Γ𝑙2Γ𝑙3 … Γ𝑙 𝑛
Γ(1 + 𝑙1 + 𝑙2 + ⋯+ 𝑙 𝑛)
ℎ𝑙1+𝑙2+⋯+𝑙 𝑛
Example 1: Prove that ∫
𝒙 𝟒(𝟏+𝒙 𝟓)
(𝟏+𝒙 𝟏𝟓)
𝒅𝒙 =
𝟏
𝟓𝟎𝟎𝟓
∞
𝟎
Solution: Let 𝐼 = ∫
𝒙 𝟒(𝟏+𝒙 𝟓)
(𝟏+𝒙) 𝟏𝟓
𝒅𝒙
∞
𝟎
 𝐼 = ∫
𝑥4
(1+𝑥)15
𝑑𝑥
∞
0
+ ∫
𝑥9
(1+𝑥)15
𝑑𝑥
∞
0
 𝐼 = 𝐼1 + 𝐼2 __________ (i)
Now, put 𝑥 =
𝑡
1+𝑡
, when 𝑥 = 0, 𝑡 = 0; when 𝑥 = ∞, 𝑡 = 1
1 + 𝑥 = 1 +
𝑡
1−𝑡
=
1
1−𝑡
 𝑑𝑥 =
𝑑𝑡
(1−𝑡)2
∴ 𝐼1 = ∫ (
𝑡
1−𝑡
)
4
. (1 − 𝑡)15
.
1
(1−𝑡)2
𝑑𝑡
1
0
= ∫ 𝑡4
(1− 𝑡)9
𝑑𝑡
1
0
= 𝛽(5,10) _______(2)
And 𝐼2 = ∫ (
𝑡
1−𝑡
)
9
. (1 − 𝑡)15
.
1
(1−𝑡)2
𝑑𝑡
1
0
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 10
= ∫ 𝑡9
(1− 𝑡)4
𝑑𝑡
1
0
= 𝛽(10,5) ________(3)
∴ 𝐼 = 𝐼1 + 𝐼2
= 𝛽(5,10) + 𝛽(10,5) [Using(2) and (3)]
= 𝛽(5,10) + 𝛽(5,10) [𝛽( 𝑚, 𝑛) = 𝛽(𝑛, 𝑚)]
= 2𝛽(5,10)
=
2Γ5Γ10
Γ15
=
2×4!×9!
14!
=
2×4×3×2×1×9!
14×13×12×11×10×9!
=
1
5005
_______ Proved.
5.3 EXERCISE:
1) Find the value of ∫
𝑥3−2𝑥4+𝑥5
(1+𝑥)7
𝑑𝑥
1
0
2) Show that ∫
𝑥 𝑚−1(1−𝑥) 𝑛−1
(𝑎+𝑥) 𝑚+𝑛
𝑑𝑥 =
𝛽(𝑚,𝑛)
𝑎 𝑛(1+𝑎) 𝑚
1
0
3) 𝛽( 𝑚 + 1, 𝑛) =
𝑚
𝑚+𝑛
𝛽(𝑚, 𝑛)
6.1 Application to Area & Volume:
 Liouville’s extension of dirichlet theorem:
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 11
∭ 𝑓(𝑥 + 𝑦 + 𝑧)𝑥 𝑙−1
𝑦 𝑚−1
𝑧 𝑛−1
𝑑𝑥 𝑑𝑦 𝑑𝑧
=
Γ(l)Γ(m)Γ(n)
Γ(l + m + n)
∫ 𝑓( 𝑢) 𝑢𝑙+𝑚+𝑛−1
𝑑𝑢
ℎ2
ℎ1
Example1: Show that ∭
𝒅𝒙 𝒅𝒚 𝒅𝒛
(𝒙+𝒚+𝒛+𝟏) 𝟑
=
𝟏
𝟐
𝒍𝒐𝒈𝟐−
𝟓
𝟏𝟔
, the integral being
takenthroughout the volume bounded by
𝒙 = 𝟎, 𝒚 = 𝟎, 𝒛 = 𝟎, 𝒙 + 𝒚 + 𝒛 = 𝟏.
Solution: By Liouville’s theorem when 0 < 𝑥 + 𝑦 + 𝑧 < 1
∭
𝑑𝑥 𝑑𝑦 𝑑𝑧
(𝑥+𝑦+𝑧+1)3
= ∭
𝑥 𝑙−1 𝑦 𝑚−1 𝑧 𝑛−1 𝑑𝑥 𝑑𝑦 𝑑𝑧
(𝑥+𝑦+𝑧+1)3
(0 ≤ 𝑥 + 𝑦 + 𝑧 ≤ 1)
=
Γ1Γ1Γ1
Γ(l+m+n)
∫
1
(u+1)3
u3−1
du
1
0
=
1
2
∫
𝑢2
(𝑢+1)3
𝑑𝑢
1
0
= ∫ [
1
𝑢+1
−
2
(𝑢+1)2
+
1
(𝑢+1)3
] 𝑑𝑢
1
0
(Partial fractions)
=
1
2
[log( 𝑢 + 1) +
2
𝑢+1
−
1
2(𝑢+1)2
]
0
1
=
1
2
[𝑙𝑜𝑔2 + 2(
1
2
− 1) − (
1
8
−
1
2
)]
=
1
2
𝑙𝑜𝑔2 −
5
16
∴ ∭
𝒅𝒙 𝒅𝒚 𝒅𝒛
(𝒙+𝒚+𝒛+𝟏) 𝟑
=
𝟏
𝟐
𝒍𝒐𝒈𝟐−
𝟓
𝟏𝟔
_______Proved.
Example 2: Find the mass of an octantof the ellipsoid
𝒙 𝟐
𝒂 𝟐
+
𝒚 𝟐
𝒃 𝟐
+
𝒛 𝟐
𝒄 𝟐
= 𝟏,
the density at any point being 𝝆 = 𝒌 𝒙 𝒚 𝒛.
Solution: Mass = ∭ 𝜌 𝑑𝑣
= ∭( 𝑘 𝑥 𝑦 𝑧) 𝑑𝑥 𝑑𝑦 𝑑𝑧
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 12
= 𝑘 ∭( 𝑥 𝑑𝑥)( 𝑦 𝑑𝑥)(𝑧 𝑑𝑧) _______(1)
Putting
𝑥2
𝑎2
= 𝑢,
𝑦2
𝑏2
= 𝑣,
𝑧2
𝑐2
= 𝑤 and 𝑢 + 𝑣 + 𝑤 = 1
So that
2𝑥 𝑑𝑥
𝑎2
= 𝑑𝑢,
2𝑦 𝑑𝑦
𝑏2
= 𝑑𝑣,
2𝑧 𝑑𝑧
𝑐2
= 𝑑𝑤
Mass= 𝑘∭ (
𝑎2 𝑑𝑢
2
)(
𝑏2 𝑑𝑣
2
)(
𝑐2 𝑑𝑤
2
)
=
𝑘 𝑎2 𝑏2 𝑐2
8
∭ 𝑑𝑢 𝑑𝑣 𝑑𝑤, Where 𝑢 + 𝑣 + 𝑤 ≤ 1
=
𝑘 𝑎2 𝑏2 𝑐2
8
∭ 𝑢𝑙−1
𝑣 𝑙−1
𝑤 𝑙−1
𝑑𝑢 𝑑𝑣 𝑑𝑤
=
𝑘 𝑎2 𝑏2 𝑐2
8
Γ1Γ1Γ1
Γ3+1
=
𝑘 𝑎2 𝑏2 𝑐2
8×6
=
𝑘 𝑎2 𝑏2 𝑐2
48
∴ 𝑴𝒂𝒔𝒔 =
𝒌 𝒂 𝟐 𝒃 𝟐 𝒄 𝟐
𝟒𝟖
Ans.
Unit-2 GAMMA, BETA FUNCTION
RAI UNIVERSITY, AHMEDABAD 13
6.2 EXERCISE:
1) Find the value of ∭ 𝑙𝑜𝑔( 𝑥 + 𝑦 + 𝑧) 𝑑𝑥 𝑑𝑦 𝑑𝑧 the integral extending
over all positive and zero values of 𝑥, 𝑦, 𝑧 subject to the condition 𝑥 +
𝑦 + 𝑧 < 1.
2) Evaluate ∭
√1−𝑥2−𝑦2−𝑧2
1+𝑥2+𝑦2+𝑧2
𝑑𝑥 𝑑𝑦 𝑑𝑧, integral being taken over all
positive values of 𝑥, 𝑦, 𝑧 such that 𝑥2
+ 𝑦2
+ 𝑧2
≤ 1.
3) Find the area and the mass contained m the first quadrant enclosed by
the curve (
𝑥
𝑎
)
𝛼
+ (
𝑦
𝑏
)
𝛽
= 1 𝑤ℎ𝑒𝑟𝑒 𝛼 > 0, 𝛽 > 0 given that density at
any point 𝑝(𝑥𝑦) is 𝑘 √ 𝑥𝑦.
7.1 REFERENCEBOOK:
1) Introduction to Engineering Mathematics
By H. K. DASS. & Dr. RAMA VERMA
2) Higher Engineering Mathematics
By B.V.RAMANA
3) A text bookof Engineering Mathematics
By N.P.BALI
4) www1.gantep.edu.tr/~olgar/C6.SP.pdf

More Related Content

PDF
Beta gamma functions
DOC
Gamma beta functions-1
PPTX
The gamma function
PPT
Gamma function
PPTX
Beta and gamma function
PDF
Gamma and betta function harsh shah
PPTX
PPTX
Bessel’s equation
Beta gamma functions
Gamma beta functions-1
The gamma function
Gamma function
Beta and gamma function
Gamma and betta function harsh shah
Bessel’s equation

What's hot (20)

PDF
Beta & Gamma Functions
PPT
Math For Physics
DOCX
B.tech ii unit-5 material vector integration
PPTX
Fourier series
PPTX
Divergence,curl,gradient
PPTX
Power Series,Taylor's and Maclaurin's Series
PPTX
Runge kutta method -by Prof.Prashant Goad(R.C.Patel Institute of Technology,...
PDF
Inverse Laplace Transform
PPTX
stirling method maths
PPT
Application of Gauss,Green and Stokes Theorem
PDF
Legendre Function
PPTX
Gradient , Directional Derivative , Divergence , Curl
PPTX
presentation on Euler and Modified Euler method ,and Fitting of curve
PDF
B.Tech-II_Unit-II
DOCX
B.tech ii unit-1 material curve tracing
PPTX
simpion's 3/8 rule
DOCX
Btech_II_ engineering mathematics_unit3
PPTX
Runge kutta
PPT
Eigenvalues and Eigenvectors
Beta & Gamma Functions
Math For Physics
B.tech ii unit-5 material vector integration
Fourier series
Divergence,curl,gradient
Power Series,Taylor's and Maclaurin's Series
Runge kutta method -by Prof.Prashant Goad(R.C.Patel Institute of Technology,...
Inverse Laplace Transform
stirling method maths
Application of Gauss,Green and Stokes Theorem
Legendre Function
Gradient , Directional Derivative , Divergence , Curl
presentation on Euler and Modified Euler method ,and Fitting of curve
B.Tech-II_Unit-II
B.tech ii unit-1 material curve tracing
simpion's 3/8 rule
Btech_II_ engineering mathematics_unit3
Runge kutta
Eigenvalues and Eigenvectors
Ad

Viewers also liked (20)

DOCX
B.tech ii unit-3 material multiple integration
DOC
Gamma & Beta functions
PDF
Multiple integrals
PPTX
Maths-double integrals
PPTX
Special functions
PDF
Gamma function for different negative numbers and its applications
PDF
09 Unif Exp Gamma
PDF
Chapter 4: Decision theory and Bayesian analysis
PDF
FRM - Level 1 Part 2 - Quantitative Methods including Probability Theory
PPT
Rectangular Coordinates, Introduction to Graphing Equations
PDF
Decision theory
PPT
Bayseian decision theory
PPTX
Gamma, Expoential, Poisson And Chi Squared Distributions
PPTX
Complex numbers polynomial multiplication
PPT
Management functions and decision making
PDF
BCA_Semester-II-Discrete Mathematics_unit-iv Graph theory
DOCX
Unit 1 Introduction
DOCX
BSC_Computer Science_Discrete Mathematics_Unit-I
DOCX
Btech_II_ engineering mathematics_unit5
PDF
B.Tech-II_Unit-I
B.tech ii unit-3 material multiple integration
Gamma & Beta functions
Multiple integrals
Maths-double integrals
Special functions
Gamma function for different negative numbers and its applications
09 Unif Exp Gamma
Chapter 4: Decision theory and Bayesian analysis
FRM - Level 1 Part 2 - Quantitative Methods including Probability Theory
Rectangular Coordinates, Introduction to Graphing Equations
Decision theory
Bayseian decision theory
Gamma, Expoential, Poisson And Chi Squared Distributions
Complex numbers polynomial multiplication
Management functions and decision making
BCA_Semester-II-Discrete Mathematics_unit-iv Graph theory
Unit 1 Introduction
BSC_Computer Science_Discrete Mathematics_Unit-I
Btech_II_ engineering mathematics_unit5
B.Tech-II_Unit-I
Ad

Similar to B.tech ii unit-2 material beta gamma function (20)

DOCX
Btech_II_ engineering mathematics_unit2
PDF
DOUBLE INTEGRAL.Introduction Numerical Problem Based on Lagrange’s Method of ...
PDF
Beta gamma functions
PDF
1586746631GAMMA BETA FUNCTIONS.pdf
PPTX
Gamma function
PPTX
Gamma function
PDF
Funcion gamma
PPTX
PresentaciónPresentación-integrales-integrales.pptx
PPTX
Ppt of aem some special function
PPTX
MATRICES AND CALCULUS.pptx
PPTX
Multiple Integrals, Gamma and Beta Functions.pptx_20250531_235537_0000.pptx
PPTX
Statistical Inference Part II: Types of Sampling Distribution
PDF
Bc4103338340
PDF
Integration (Part 1)bbbbbbbbb_SA (1).pdf
PDF
Evaluating definite integrals
PDF
Some Continued Mock Theta Functions from Ramanujan’s Lost Notebook (IV)
PDF
Math Integral Calculus Lecture Buet Civil
PDF
IJERD (www.ijerd.com) International Journal of Engineering Research and Devel...
PDF
Simultaneous triple series equations
Btech_II_ engineering mathematics_unit2
DOUBLE INTEGRAL.Introduction Numerical Problem Based on Lagrange’s Method of ...
Beta gamma functions
1586746631GAMMA BETA FUNCTIONS.pdf
Gamma function
Gamma function
Funcion gamma
PresentaciónPresentación-integrales-integrales.pptx
Ppt of aem some special function
MATRICES AND CALCULUS.pptx
Multiple Integrals, Gamma and Beta Functions.pptx_20250531_235537_0000.pptx
Statistical Inference Part II: Types of Sampling Distribution
Bc4103338340
Integration (Part 1)bbbbbbbbb_SA (1).pdf
Evaluating definite integrals
Some Continued Mock Theta Functions from Ramanujan’s Lost Notebook (IV)
Math Integral Calculus Lecture Buet Civil
IJERD (www.ijerd.com) International Journal of Engineering Research and Devel...
Simultaneous triple series equations

More from Rai University (20)

PDF
Brochure Rai University
PPT
Mm unit 4point2
PPT
Mm unit 4point1
PPT
Mm unit 4point3
PPT
Mm unit 3point2
PPTX
Mm unit 3point1
PPTX
Mm unit 2point2
PPT
Mm unit 2 point 1
PPT
Mm unit 1point3
PPT
Mm unit 1point2
PPTX
Mm unit 1point1
DOCX
Bdft ii, tmt, unit-iii, dyeing & types of dyeing,
PPTX
Bsc agri 2 pae u-4.4 publicrevenue-presentation-130208082149-phpapp02
PPTX
Bsc agri 2 pae u-4.3 public expenditure
PPTX
Bsc agri 2 pae u-4.2 public finance
PPS
Bsc agri 2 pae u-4.1 introduction
PPT
Bsc agri 2 pae u-3.3 inflation
PPTX
Bsc agri 2 pae u-3.2 introduction to macro economics
PPTX
Bsc agri 2 pae u-3.1 marketstructure
PPTX
Bsc agri 2 pae u-3 perfect-competition
Brochure Rai University
Mm unit 4point2
Mm unit 4point1
Mm unit 4point3
Mm unit 3point2
Mm unit 3point1
Mm unit 2point2
Mm unit 2 point 1
Mm unit 1point3
Mm unit 1point2
Mm unit 1point1
Bdft ii, tmt, unit-iii, dyeing & types of dyeing,
Bsc agri 2 pae u-4.4 publicrevenue-presentation-130208082149-phpapp02
Bsc agri 2 pae u-4.3 public expenditure
Bsc agri 2 pae u-4.2 public finance
Bsc agri 2 pae u-4.1 introduction
Bsc agri 2 pae u-3.3 inflation
Bsc agri 2 pae u-3.2 introduction to macro economics
Bsc agri 2 pae u-3.1 marketstructure
Bsc agri 2 pae u-3 perfect-competition

Recently uploaded (20)

PDF
102 student loan defaulters named and shamed – Is someone you know on the list?
PDF
RMMM.pdf make it easy to upload and study
PDF
O7-L3 Supply Chain Operations - ICLT Program
PDF
01-Introduction-to-Information-Management.pdf
PDF
2.FourierTransform-ShortQuestionswithAnswers.pdf
PDF
Module 4: Burden of Disease Tutorial Slides S2 2025
PPTX
IMMUNITY IMMUNITY refers to protection against infection, and the immune syst...
PPTX
1st Inaugural Professorial Lecture held on 19th February 2020 (Governance and...
PDF
The Lost Whites of Pakistan by Jahanzaib Mughal.pdf
PDF
grade 11-chemistry_fetena_net_5883.pdf teacher guide for all student
PDF
Black Hat USA 2025 - Micro ICS Summit - ICS/OT Threat Landscape
PDF
FourierSeries-QuestionsWithAnswers(Part-A).pdf
PPTX
GDM (1) (1).pptx small presentation for students
PPTX
Institutional Correction lecture only . . .
PDF
Basic Mud Logging Guide for educational purpose
PPTX
human mycosis Human fungal infections are called human mycosis..pptx
PPTX
Renaissance Architecture: A Journey from Faith to Humanism
PPTX
Cell Types and Its function , kingdom of life
PPTX
school management -TNTEU- B.Ed., Semester II Unit 1.pptx
PPTX
Pharmacology of Heart Failure /Pharmacotherapy of CHF
102 student loan defaulters named and shamed – Is someone you know on the list?
RMMM.pdf make it easy to upload and study
O7-L3 Supply Chain Operations - ICLT Program
01-Introduction-to-Information-Management.pdf
2.FourierTransform-ShortQuestionswithAnswers.pdf
Module 4: Burden of Disease Tutorial Slides S2 2025
IMMUNITY IMMUNITY refers to protection against infection, and the immune syst...
1st Inaugural Professorial Lecture held on 19th February 2020 (Governance and...
The Lost Whites of Pakistan by Jahanzaib Mughal.pdf
grade 11-chemistry_fetena_net_5883.pdf teacher guide for all student
Black Hat USA 2025 - Micro ICS Summit - ICS/OT Threat Landscape
FourierSeries-QuestionsWithAnswers(Part-A).pdf
GDM (1) (1).pptx small presentation for students
Institutional Correction lecture only . . .
Basic Mud Logging Guide for educational purpose
human mycosis Human fungal infections are called human mycosis..pptx
Renaissance Architecture: A Journey from Faith to Humanism
Cell Types and Its function , kingdom of life
school management -TNTEU- B.Ed., Semester II Unit 1.pptx
Pharmacology of Heart Failure /Pharmacotherapy of CHF

B.tech ii unit-2 material beta gamma function

  • 1. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 1 Unit-II: GAMMA, BETA FUNCTION Sr. No. Name of the Topic Page No. 1 Definition of Gamma function 2 2 Examples Based on Gamma Function 3 3 Beta function 5 4 Relation between Beta and Gamma Functions 5 5 Dirichlet’s Integral 9 6 Application to Area & Volume: Liouville’s extension of dirichlet theorem 11 7 Reference Book 13
  • 2. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 2 GAMMA, BETA FUNCTION  The Gamma function and Beta functions belong to the category of the special transcendental functions and are defined in terms of improper definite integrals. 1.1 Definition of Gamma function : The gamma function is denoted and defined by the integral Γ𝑚 = ∫ 𝑒−𝑥 𝑥 𝑚−1 𝑑𝑥 (𝑚 > 0) ∞ 0 1.2 Properties of Gamma function : 1) Γ( 𝑚 + 1) = 𝑚Γ𝑚 2) Γ( 𝑚 + 1) = 𝑚! When m is a positive integer. 3) Γ( 𝑚 + 𝑎) = ( 𝑚 + 𝑎 − 1)( 𝑚 + 𝑎 − 2)……… 𝑎Γ𝑎, when n is a positive integer. 4) Γ𝑚 = 2 ∫ 𝑒−𝑥2 𝑥2𝑚−1 𝑑𝑥 ( 𝑚 > 0) ∞ 0 5) Γ𝑚 𝑡 𝑚 = ∫ 𝑒−𝑡𝑥 𝑥 𝑚−1 𝑑𝑥 ( 𝑚 > 0) ∞ 0 6) Γ 1 2 = √ 𝜋 7) ∫ 𝑒−𝑥2 𝑑𝑥 = √𝜋 2 ∞ 0 8) ∫ 𝑥 𝑛 (𝑙𝑜𝑔 𝑥) 𝑚 𝑑𝑥 = (−1) 𝑚 ( 𝑛+1) 𝑚+1 Γ(𝑚 + 1) 1 0 2.1 Examples Based on Gamma Function: Example 1: Evaluate 𝚪(− 𝟏 𝟐 ). Solution: We know that Γ( 𝑚 + 1) = 𝑚Γ𝑚
  • 3. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 3  Γ (− 1 2 + 1) = − 1 2 Γ (− 1 2 )  Γ ( 1 2 ) = − 1 2 Γ(− 1 2 )  √ 𝜋 = − 1 2 Γ (− 1 2 ) ∴ 𝚪(− 𝟏 𝟐 ) = −𝟐√ 𝝅. __________Ans. Example 2: Evaluate ∫ √ 𝒙𝟒 𝒆−√𝒙 𝒅𝒙 ∞ 𝟎 Solution: Let 𝐼 = ∫ 𝑥 1 4 𝑒−√𝑥 𝑑𝑥 ∞ 0 __________(i) Putting √ 𝑥 = 𝑡 ⟹ 𝑥 = 𝑡2 so that 𝑑𝑥 = 2𝑡 in (i), we get 𝐼 = ∫ 𝑡1 2⁄ 𝑒−𝑡 2𝑡 𝑑𝑡 ∞ 0 = 2∫ 𝑡3 2⁄ 𝑒−𝑡 𝑑𝑡 ∞ 0 = 2∫ 𝑡 5 2 −1 𝑒−𝑡 𝑑𝑡 ∞ 0 = 2Γ( 5 2 ) = (2 × 3 2 )Γ ( 3 2 ) = (2 × 3 2 × 1 2 )Γ ( 1 2 ) = 3 2 √ 𝜋 ∴ ∫ √ 𝒙𝟒 𝒆−√𝒙 𝒅𝒙 ∞ 𝟎 = 𝟑 𝟐 √ 𝝅 ________Ans. Example 3: Evaluate ∫ 𝒙 𝒂 𝒂 𝒙 𝒅𝒙 ∞ 𝟎 . Solution: Let 𝐼 = ∫ 𝑥 𝑎 𝑎 𝑥 𝑑𝑥 ∞ 0 _______ (i) Putting 𝑎 𝑥 = 𝑒 𝑡
  • 4. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 4 ⟹ 𝑥 log 𝑎 = 𝑡 ⟹ 𝑥 = 1 log 𝑎 ⟹ 𝑑𝑥 = 𝑑𝑡 log 𝑎 in (i), we have 𝐼 = ∫ ( 𝑡 log 𝑎 ) 𝑎 𝑒−𝑡∞ 0 𝑑𝑡 log 𝑎 = 1 (log 𝑎) 𝑎+1 ∫ 𝑒−𝑡 𝑡 𝑎 𝑑𝑡 ∞ 0 = 1 (log 𝑎) 𝑎+1 ∫ 𝑡( 𝑎+1)−1 𝑒−𝑡 𝑑𝑡 ∞ 0 = 1 (log 𝑎) 𝑎+1 Γ(𝑎 + 1) ∴ ∫ 𝒙 𝒂 𝒂 𝒙 𝒅𝒙 ∞ 𝟎 = 𝟏 ( 𝐥𝐨𝐠 𝒂) 𝒂+𝟏 𝚪(𝒂 + 𝟏) ________ Ans. Example 4: Prove that ∫ ( 𝒙 𝒍𝒐𝒈𝒙) 𝟒 𝒅𝒙 = 𝟒! 𝟓 𝟓 𝟏 𝟎 Solution: We know that ∫ 𝑥 𝑛 (𝑙𝑜𝑔 𝑥) 𝑚 𝑑𝑥 = (−1) 𝑚 ( 𝑛+1) 𝑚+1 Γ(𝑚 + 1) 1 0 _______(i) Now, ∫ ( 𝑥 𝑙𝑜𝑔𝑥)4 𝑑𝑥 = 1 0 ∫ 𝑥41 0 ( 𝑙𝑜𝑔𝑥)4 𝑑𝑥 Putting 𝑛 = 𝑚 = 4 in (i), we get ∫ 𝑥4 1 0 ( 𝑙𝑜𝑔𝑥)4 𝑑𝑥 = (−1)4 (4 + 1)4+1 Γ(4 + 1) = Γ5 55 = 4! 55 __________ proved. 2.2 EXERCISE:
  • 5. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 5 1) Evaluate: (a) Γ(− 3 2 ) (b) Γ ( 7 2 ) (c)Γ(0) 2) ∫ 𝑒−ℎ2 𝑥2 𝑑𝑥 ∞ 0 3) ∫ 𝑑𝑥 √−𝑙𝑜𝑔𝑥 1 0 4) ∫ ( 𝑥 𝑙𝑜𝑔𝑥)3 𝑑𝑥 1 0 3.1 BETA FUNCTION: Definition: The Beta function denoted by 𝛽( 𝑚, 𝑛) or 𝐵(𝑚, 𝑛) is defined as 𝐵( 𝑚, 𝑛) = ∫ 𝑥 𝑚−1 (1 − 𝑥) 𝑛−1 𝑑𝑥, (𝑚 > 0, 𝑛 > 0) 1 0 3.2 Properties of Beta function: 1) B(m,n)= B(n,m) 2) 𝐵( 𝑚, 𝑛) = 2 ∫ 𝑠𝑖𝑛2𝑚−1 𝜃 𝑐𝑜𝑠2𝑛−1 𝜃 𝑑𝜃 𝜋 2⁄ 0 3) 𝐵( 𝑚, 𝑛) = ∫ 𝑥 𝑚−1 (1+𝑥) 𝑚+𝑛 𝑑𝑥 ∞ 0 4) 𝐵( 𝑚, 𝑛) = ∫ 𝑥 𝑚−1+𝑥 𝑛−1 (1+𝑥) 𝑚+𝑛 𝑑𝑥 1 0 4.1 RelationbetweenBeta and Gamma Functions: Relation between Beta and gamma functions is 𝛽( 𝑚, 𝑛) = Γm .Γn Γ(m+n)  Using above relation we can derive following results:  ∫ 𝑠𝑖𝑛 𝑝 𝜃 𝑐𝑜𝑠 𝑝 𝜃 𝑑𝜃 = 1 2 𝛽 ( 𝑝+1 2 , 𝑞+1 2 ) = Γ( 𝑝+1 2 ).( 𝑞+1 2 ) 2Γ( 𝑝+𝑞+2 2 ) 𝜋 2⁄ 0  Γ ( 1 2 ) = √ 𝜋  Euler’s formula: Γ𝑛 . Γ(1 − 𝑛) = 𝜋 sin 𝑛𝜋  Duplication formula:
  • 6. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 6 Γ𝑛 . Γ(𝑛 + 1 2 ) = √𝜋 Γ(2𝑛) 22𝑛−1 4.2 EXAMPLES: Example 1: Evaluate ∫ 𝒙 𝟒 (𝟏− √ 𝒙) 𝟓 𝒅𝒙 𝟏 𝟎 Solution: Let √ 𝑥 = 𝑡 ⟹ 𝑥 = 𝑡2 so that 𝑑𝑥 = 2𝑡 𝑑𝑡 ∫ 𝑥4 (1− √ 𝑥) 5 𝑑𝑥 = 1 0 ∫( 𝑡2)4 (1 − 𝑡)5 (2𝑡 𝑑𝑡) 1 0 = 2 ∫ 𝑡9 (1 − 𝑡)5 𝑑𝑡 1 0 = 2 𝐵(10,6) = 2 Γ10 Γ6 Γ16 = 2 × 9!5! 15! = 2×1×2×3×4×5 15×14×13×12×11×10 = 1 11×13×7×15 = 1 15015 ∴ ∫ 𝑥4 (1 − √ 𝑥) 5 𝑑𝑥 = 1 0 1 15015 _________ Ans. Example 2: Find the value of 𝚪 ( 𝟏 𝟐 ). Solution: We know that, ∫ 𝑠𝑖𝑛 𝑝 𝜃 𝑐𝑜𝑠 𝑝 𝜃 𝑑𝜃 = Γ( 𝑝+1 2 ).( 𝑞+1 2 ) 2Γ( 𝑝+𝑞+2 2 ) 𝜋 2⁄ 0 Putting 𝑝 = 𝑞 = 0, we get ∫ 𝑑𝜃 = 𝚪( 𝟏 𝟐 ) 𝚪( 𝟏 𝟐 ) 2 𝚪𝟏 𝜋 2 0  [ 𝜃]0 𝜋 2⁄ = 1 2 (Γ 1 2 ) 2
  • 7. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 7  𝜋 2 = 1 2 (Γ 1 2 ) 2  (Γ 1 2 ) 2 = 𝜋  Γ ( 1 2 ) = √ 𝜋 _______Ans. Example 3: show that ∫ √ 𝒄𝒐𝒕𝜽 𝒅𝜽 = 𝟏 𝟐 𝚪( 𝟏 𝟒 ) 𝚪 ( 𝟑 𝟒 ) 𝝅 𝟐 𝟎 Solution: We know that, ∫ 𝑠𝑖𝑛 𝑝 𝜃 𝑐𝑜𝑠 𝑝 𝜃 𝑑𝜃 = Γ( 𝑝+1 2 ).( 𝑞+1 2 ) 2Γ( 𝑝+𝑞+2 2 ) 𝜋 2⁄ 0 ∫ √ 𝑐𝑜𝑡𝜃𝑑𝜃 = ∫ 𝑐𝑜𝑠1 2⁄ 𝜃 𝑠𝑖𝑛1 2⁄ 𝜃 𝑑𝜃 𝜋 2 0 𝜋 2 0 = ∫ 𝑠𝑖𝑛−1 2⁄ 𝜃 𝜋 2 0 𝑐𝑜𝑠1 2⁄ 𝜃 𝑑𝜃 On applying formula (1), we have ∫ √ 𝑐𝑜𝑡𝜃𝑑𝜃 = Γ( − 1 2 +1 2 ) Γ( 1 2 +1 2 ) 2Γ( − 1 2 + 1 2 +2 2 ) 𝜋 2 0 = Γ( 1 4 ) Γ( 3 4 ) 2 Γ(1) = 1 2 Γ ( 1 4 )Γ ( 3 4 ) ∴ ∫ √ 𝑐𝑜𝑡𝜃 𝑑𝜃 = 1 2 Γ ( 1 4 )Γ ( 3 4 ) 𝜋 2 0 __________Ans. Example 4: Evaluate ∫ ( 𝟏 + 𝒙) 𝒑−𝟏 ( 𝟏 − 𝒙) 𝒒−𝟏 𝒅𝒙 +𝟏 −𝟏 Solution: Put 𝑥 = 2cos 2𝜃, then 𝑑𝑥 = −2sin 2𝜃 𝑑𝜃 in ∫ (1 + 𝑥) 𝑝−1 (1 − 𝑥) 𝑞−1 𝑑𝑥 +1 −1 = ∫ (1 + 𝑐𝑜𝑠2𝜃) 𝑝−1(1 − 𝑐𝑜𝑠2𝜃) 𝑞−1(−2𝑠𝑖𝑛2𝜃) 0 𝜋 2 = ∫ (1 + 2𝑐𝑜𝑠2 𝜃 − 1) 𝑝−1(1 − 1 + 2𝑠𝑖𝑛2 𝜃) 𝑞−1(−4𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃 𝑑𝜃) 0 𝜋 2 = 4∫ 2 𝑝−1 𝑐𝑜𝑠2𝑝−2 𝜃 . 2 𝑞−1 𝑠𝑖𝑛2𝑞−2 𝜃 . 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜃 𝑑𝜃 𝜋 2 0
  • 8. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 8 = 2 𝑝+𝑞 ∫ 𝑠𝑖𝑛2𝑞−1 𝜃 𝑐𝑜𝑠2𝑝−1 𝜃 ∞ 0 𝑑𝜃 = 2 𝑝+𝑞 Γ( 2𝑞 2 ) Γ( 2𝑝 2 ) 2Γ( 2𝑝+2𝑞 2 ) = 2 𝑝+𝑞−1 Γ( 𝑝) Γ( 𝑞) Γ( 𝑝+𝑞) __________Ans. Example 5: Show that 𝚪( 𝒏) 𝚪( 𝟏− 𝒏) = 𝝅 𝒔𝒊𝒏 𝒏𝝅 (𝟎 < 𝑛 < 1) Solution: We know that 𝛽( 𝑚, 𝑛) = ∫ 𝑥 𝑛−1 (1 + 𝑥) 𝑚+𝑛 𝑑𝑥 ∞ 0 Γ𝑚 Γ𝑛 Γ(𝑚+𝑛) = ∫ 𝑥 𝑛−1 (1+𝑥) 𝑚+𝑛 𝑑𝑥 ∞ 0 Putting 𝑚 + 𝑛 = 1 𝑜𝑟 𝑚 = 1 − 𝑛, we get Γ(1−𝑛) Γ𝑛 Γ1 = ∫ 𝑥 𝑛−1 (1+𝑥)1 𝑑𝑥 ∞ 0 Γ(1 − 𝑛)Γ𝑛 = ∫ 𝑥 𝑛−1 1+𝑥 𝑑𝑥 ∞ 0 [∵ ∫ 𝑥 𝑛−1 1+𝑥 𝑑𝑥 ∞ 0 = 𝜋 𝑠𝑖𝑛 𝑛𝜋 ] ∴ Γ( 𝑛)Γ(1− 𝑛) = 𝜋 𝑠𝑖𝑛 𝑛𝜋 ______proved. 4.3 EXERCISE: 1) Evaluate ∫ (1 − 𝑥3)−1 2⁄ 𝑑𝑥 1 0 2) Evaluate ∫ 𝑥 𝑚−1+𝑥 𝑛−1 (1+𝑥) 𝑚+𝑛 𝑑𝑥 1 0 3) Evaluate ∫ ( 𝑥3 1−𝑥3 ) 1 2 𝑑𝑥 1 0 4) Prove that Γ ( 1 4 ) Γ ( 3 4 ) = 𝜋√2 5) Show that 𝛽( 𝑝, 𝑞) = 𝛽( 𝑝 + 1, 𝑞) + (𝑝, 𝑞 + 1) 5.1 DIRICHLET’S INTEGRAL: If 𝑙, 𝑚, 𝑛 are all positive, then the triple integral ∭ 𝑥 𝑙−1 𝑦 𝑚−1 𝑧 𝑛−1 𝑑𝑥 𝑑𝑦 𝑑𝑧 𝑉 = Γ(l)Γ(m)Γ(n) Γ(𝑙 + 𝑚 + 𝑛 + 1)
  • 9. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 9 Where V is the region 𝑥 ≥ 0, 𝑦 ≥ 0, 𝑧 ≥ 0 and 𝑥 + 𝑦 + 𝑧 ≤ 1. Note: ∭ 𝑥 𝑙−1 𝑦 𝑚−1 𝑧 𝑛−1 𝑑𝑥 𝑑𝑦 𝑑𝑧𝑉 = Γ(l)Γ(m)Γ(n) Γ(𝑙+𝑚+𝑛+1) ℎ𝑙+𝑚+𝑛 Where V is the domain, 𝑥 ≥ 0, 𝑦 ≥ 0, 𝑧 ≥ 0 and 𝑥 + 𝑦 + 𝑧 ≤ ℎ 5.2 Corollary: Dirichlet’s theorem for n variables, the theorem status that ∭…∫ 𝑥1 𝑙1−1 𝑥2 𝑙2−1 … 𝑥 𝑛 𝑙 𝑛−1 𝑑𝑥1 𝑑𝑥2 𝑑𝑥3 … 𝑑𝑥 𝑛 = Γ𝑙1Γ𝑙2Γ𝑙3 … Γ𝑙 𝑛 Γ(1 + 𝑙1 + 𝑙2 + ⋯+ 𝑙 𝑛) ℎ𝑙1+𝑙2+⋯+𝑙 𝑛 Example 1: Prove that ∫ 𝒙 𝟒(𝟏+𝒙 𝟓) (𝟏+𝒙 𝟏𝟓) 𝒅𝒙 = 𝟏 𝟓𝟎𝟎𝟓 ∞ 𝟎 Solution: Let 𝐼 = ∫ 𝒙 𝟒(𝟏+𝒙 𝟓) (𝟏+𝒙) 𝟏𝟓 𝒅𝒙 ∞ 𝟎  𝐼 = ∫ 𝑥4 (1+𝑥)15 𝑑𝑥 ∞ 0 + ∫ 𝑥9 (1+𝑥)15 𝑑𝑥 ∞ 0  𝐼 = 𝐼1 + 𝐼2 __________ (i) Now, put 𝑥 = 𝑡 1+𝑡 , when 𝑥 = 0, 𝑡 = 0; when 𝑥 = ∞, 𝑡 = 1 1 + 𝑥 = 1 + 𝑡 1−𝑡 = 1 1−𝑡  𝑑𝑥 = 𝑑𝑡 (1−𝑡)2 ∴ 𝐼1 = ∫ ( 𝑡 1−𝑡 ) 4 . (1 − 𝑡)15 . 1 (1−𝑡)2 𝑑𝑡 1 0 = ∫ 𝑡4 (1− 𝑡)9 𝑑𝑡 1 0 = 𝛽(5,10) _______(2) And 𝐼2 = ∫ ( 𝑡 1−𝑡 ) 9 . (1 − 𝑡)15 . 1 (1−𝑡)2 𝑑𝑡 1 0
  • 10. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 10 = ∫ 𝑡9 (1− 𝑡)4 𝑑𝑡 1 0 = 𝛽(10,5) ________(3) ∴ 𝐼 = 𝐼1 + 𝐼2 = 𝛽(5,10) + 𝛽(10,5) [Using(2) and (3)] = 𝛽(5,10) + 𝛽(5,10) [𝛽( 𝑚, 𝑛) = 𝛽(𝑛, 𝑚)] = 2𝛽(5,10) = 2Γ5Γ10 Γ15 = 2×4!×9! 14! = 2×4×3×2×1×9! 14×13×12×11×10×9! = 1 5005 _______ Proved. 5.3 EXERCISE: 1) Find the value of ∫ 𝑥3−2𝑥4+𝑥5 (1+𝑥)7 𝑑𝑥 1 0 2) Show that ∫ 𝑥 𝑚−1(1−𝑥) 𝑛−1 (𝑎+𝑥) 𝑚+𝑛 𝑑𝑥 = 𝛽(𝑚,𝑛) 𝑎 𝑛(1+𝑎) 𝑚 1 0 3) 𝛽( 𝑚 + 1, 𝑛) = 𝑚 𝑚+𝑛 𝛽(𝑚, 𝑛) 6.1 Application to Area & Volume:  Liouville’s extension of dirichlet theorem:
  • 11. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 11 ∭ 𝑓(𝑥 + 𝑦 + 𝑧)𝑥 𝑙−1 𝑦 𝑚−1 𝑧 𝑛−1 𝑑𝑥 𝑑𝑦 𝑑𝑧 = Γ(l)Γ(m)Γ(n) Γ(l + m + n) ∫ 𝑓( 𝑢) 𝑢𝑙+𝑚+𝑛−1 𝑑𝑢 ℎ2 ℎ1 Example1: Show that ∭ 𝒅𝒙 𝒅𝒚 𝒅𝒛 (𝒙+𝒚+𝒛+𝟏) 𝟑 = 𝟏 𝟐 𝒍𝒐𝒈𝟐− 𝟓 𝟏𝟔 , the integral being takenthroughout the volume bounded by 𝒙 = 𝟎, 𝒚 = 𝟎, 𝒛 = 𝟎, 𝒙 + 𝒚 + 𝒛 = 𝟏. Solution: By Liouville’s theorem when 0 < 𝑥 + 𝑦 + 𝑧 < 1 ∭ 𝑑𝑥 𝑑𝑦 𝑑𝑧 (𝑥+𝑦+𝑧+1)3 = ∭ 𝑥 𝑙−1 𝑦 𝑚−1 𝑧 𝑛−1 𝑑𝑥 𝑑𝑦 𝑑𝑧 (𝑥+𝑦+𝑧+1)3 (0 ≤ 𝑥 + 𝑦 + 𝑧 ≤ 1) = Γ1Γ1Γ1 Γ(l+m+n) ∫ 1 (u+1)3 u3−1 du 1 0 = 1 2 ∫ 𝑢2 (𝑢+1)3 𝑑𝑢 1 0 = ∫ [ 1 𝑢+1 − 2 (𝑢+1)2 + 1 (𝑢+1)3 ] 𝑑𝑢 1 0 (Partial fractions) = 1 2 [log( 𝑢 + 1) + 2 𝑢+1 − 1 2(𝑢+1)2 ] 0 1 = 1 2 [𝑙𝑜𝑔2 + 2( 1 2 − 1) − ( 1 8 − 1 2 )] = 1 2 𝑙𝑜𝑔2 − 5 16 ∴ ∭ 𝒅𝒙 𝒅𝒚 𝒅𝒛 (𝒙+𝒚+𝒛+𝟏) 𝟑 = 𝟏 𝟐 𝒍𝒐𝒈𝟐− 𝟓 𝟏𝟔 _______Proved. Example 2: Find the mass of an octantof the ellipsoid 𝒙 𝟐 𝒂 𝟐 + 𝒚 𝟐 𝒃 𝟐 + 𝒛 𝟐 𝒄 𝟐 = 𝟏, the density at any point being 𝝆 = 𝒌 𝒙 𝒚 𝒛. Solution: Mass = ∭ 𝜌 𝑑𝑣 = ∭( 𝑘 𝑥 𝑦 𝑧) 𝑑𝑥 𝑑𝑦 𝑑𝑧
  • 12. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 12 = 𝑘 ∭( 𝑥 𝑑𝑥)( 𝑦 𝑑𝑥)(𝑧 𝑑𝑧) _______(1) Putting 𝑥2 𝑎2 = 𝑢, 𝑦2 𝑏2 = 𝑣, 𝑧2 𝑐2 = 𝑤 and 𝑢 + 𝑣 + 𝑤 = 1 So that 2𝑥 𝑑𝑥 𝑎2 = 𝑑𝑢, 2𝑦 𝑑𝑦 𝑏2 = 𝑑𝑣, 2𝑧 𝑑𝑧 𝑐2 = 𝑑𝑤 Mass= 𝑘∭ ( 𝑎2 𝑑𝑢 2 )( 𝑏2 𝑑𝑣 2 )( 𝑐2 𝑑𝑤 2 ) = 𝑘 𝑎2 𝑏2 𝑐2 8 ∭ 𝑑𝑢 𝑑𝑣 𝑑𝑤, Where 𝑢 + 𝑣 + 𝑤 ≤ 1 = 𝑘 𝑎2 𝑏2 𝑐2 8 ∭ 𝑢𝑙−1 𝑣 𝑙−1 𝑤 𝑙−1 𝑑𝑢 𝑑𝑣 𝑑𝑤 = 𝑘 𝑎2 𝑏2 𝑐2 8 Γ1Γ1Γ1 Γ3+1 = 𝑘 𝑎2 𝑏2 𝑐2 8×6 = 𝑘 𝑎2 𝑏2 𝑐2 48 ∴ 𝑴𝒂𝒔𝒔 = 𝒌 𝒂 𝟐 𝒃 𝟐 𝒄 𝟐 𝟒𝟖 Ans.
  • 13. Unit-2 GAMMA, BETA FUNCTION RAI UNIVERSITY, AHMEDABAD 13 6.2 EXERCISE: 1) Find the value of ∭ 𝑙𝑜𝑔( 𝑥 + 𝑦 + 𝑧) 𝑑𝑥 𝑑𝑦 𝑑𝑧 the integral extending over all positive and zero values of 𝑥, 𝑦, 𝑧 subject to the condition 𝑥 + 𝑦 + 𝑧 < 1. 2) Evaluate ∭ √1−𝑥2−𝑦2−𝑧2 1+𝑥2+𝑦2+𝑧2 𝑑𝑥 𝑑𝑦 𝑑𝑧, integral being taken over all positive values of 𝑥, 𝑦, 𝑧 such that 𝑥2 + 𝑦2 + 𝑧2 ≤ 1. 3) Find the area and the mass contained m the first quadrant enclosed by the curve ( 𝑥 𝑎 ) 𝛼 + ( 𝑦 𝑏 ) 𝛽 = 1 𝑤ℎ𝑒𝑟𝑒 𝛼 > 0, 𝛽 > 0 given that density at any point 𝑝(𝑥𝑦) is 𝑘 √ 𝑥𝑦. 7.1 REFERENCEBOOK: 1) Introduction to Engineering Mathematics By H. K. DASS. & Dr. RAMA VERMA 2) Higher Engineering Mathematics By B.V.RAMANA 3) A text bookof Engineering Mathematics By N.P.BALI 4) www1.gantep.edu.tr/~olgar/C6.SP.pdf