2. What do we study?
• Triangles Definition
• Types of Triangles
• Types of triangles on the basis of sides
• Types of triangles on the basis of angles
• Properties of triangles
• Triangle inequality theroem
• Pythagoras theorem
3. Triangle Definition
• A three sided closed figure is called Triangle.
• A triangle has three sides, three angles and three vertices.
• All three sides and angles are called six elements of the triangle.
4. Types of triangles
Types of triangles on the basis of sides
Scalene triangle
Isosceles triangle
Equilateral triangle
Types of triangles on the basis of angles
Acute angled triangle
Right angled triangle
Obtuse angled triangle
5. Types of triangles on the basis of sides
Scalene Triangle
If all the sides of triangle
are unequal they are called
scalene triangle.
Isosceles Triangle
A triangle having its two sides equal is
called an isosceles triangle.
In an isosceles triangle the angles
opposite to the equal sides are also equal.
In the triangle AB = AC,
therefore
angle ABC = angle ACB
Equilateral Triangle
A triangle having all its
three sides equal is called
an Equilateral Triangle.
All the angles of an
equilateral triangle are
equal and each of them is
equal to 60°.
6. Types of triangles on the basis of angles
Acute angled
Triangle
If all the three angles of a
triangle acute (i.e. less
than 90o
) is called acute
angled triangle.
An Equilateral triangle is
always an acute angled
triangle.
Right angled Triangle
A triangle having one of the angle equal
to 90o
is called an right angled triangle.
No triangle can contain more than one
right angled triangle.
A right angled triangle having two sides
equal is called a right angled isosceles
triangle, and in it the remaining two
angles are equal to 45°
Obtuse angled
Triangle
A triangle having one of
the angle is obtuse (i.e.
more than 90o
) is called an
obtuse angled triangle.
The remaining two angles
of an obtuse angled
triangle are acute.
