math project term 2.ppt

Finding Area and
Perimeter of Polygons
Suliman al suliman
10am4

Area
• Definition:
• The number of
square units
needed to cover a
surface.
(INSIDE)
• Length x width

Perimeter
• Definition:
The sum of the
length of all the
sides of a
polygon.

Base
• Definition:
• A side or face
of a figure on
which the
figure stands.

Height
• Definition:
• The distance
from the bottom
to the top of a
figure.

Width
• Definition:
• How wide a
figure is from
side to side.

Length
• Definition:
• The measure of
the distance
across an
figure.

Finding area of an irregular figure
• Box the object in then
count the length and
the width of the “box”.
• Example:
• Length = 4
• Width = 5

Hint: Length x width=area
What is the area of the
box?

Hint: Length x width=area
What is the area of the
box?
Right!
4x5=20

• How many squares are
there in the box that
are not shaded?

• How many squares are
there in the box that
are not shaded.
• Right!
• 6 squares

The area of the object is
the area of the “box”
(20) minus the squares
that are are not shaded
(6).

The area of the object is
20-6= 14
The area of the irregular
figure is 14.
*This method can be
used instead of
counting all the
squares.

Finding perimeter of a figure
• Perimeter: distance
around an object.
• In this case the Box.

• For this figure the
length is 4 and the
width is 5. You have
two 4’s and two 5’s.
• The perimeter is
• 2x4 + 2x5 = perimeter

• Multiply first, then
add:
• 8 + 10 =

• Multiply first, then
add:
• 8 + 10 = 18
• The perimeter of the
box is 18.

18 is the perimeter of the
box. So what?
We want to know the
perimeter of the
figure.Do we know the
perimeter of the
figure?

• Yes, the perimeters are
the same.
• The blue is the
perimeter of the
figure.
• The red is the
perimeter of the box.

That trick does not
work all the time.
Sometimes you may
have to count the side
and add.
What is the perimeter
of this figure?

What is the perimeter
of this figure?

Right 20!
10 on top and bottom
10 on the right and left

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