Facts about Area of Shapes

Dr. Kent Bryant5/2011

SQUARE

IF A SQUARE HAS SIDES WITH LENGTH L THEN

AREA = L X L

EG. WHAT IS THE AREA OF A SQUARE WITH LENGTH 20 cm?

Area = 20 cm X 20 cm = 400 cm2

L

L

RECTANGLE

L

W

IF A RECTANGLE HAS LENGTH L AND WIDTH W

A = L X W

EG. WHAT IS THE AREA OF A RECTANGLE WITH LENGTH 20cm AND WIDTH 40cm?

Area =20 cm x 40 cm = 800 cm2

Triangle

H

BIF A TRIANGLE HAS HEIGHT H AND BASE B

AREA = ½ B X H

EG. WHAT IS THE AREA OF A TRIANGLE WITH HEIGHT 20 cm AND BASE 15 cm?

Area = ½ x 20 x 15 – 150 cm2

Circumference of a Circle

The circumference of a circle is the distance around the circle

Circumference = Diameter X π (C = π d) π = 3.14Circumference = 2πr (r = radius)

What is the circumference of a circle with radius 5 cm?

C = 2πr = 2 X 3.14 X 5 = 31.4 cm

The diameter of a circle is the distance across the circle through the center point.

The radius of a circle is the distance from the center to the outer edge of the circle.

Diameter = 2 X radius

Area of a Circle

If a circle has a radius R then

Area = π R2

Eg. What is the area of a circle with radius 10 cm?

Area = 3.14 X 10 X 10 = 314 cm2

R

Area of Parallelogram

B

B

H

If a Parallelogram has height H and a base length of B then

Area -= B X H

Eg. What is the area of a Parallelogram with Height 10 cm and Base length 20cm?

Area – B X H = 20 cm X 10 cm =200 cm2

What about Irregular Shapes?

How do you find the area of this shape?

First – Break shape into smaller REGULAR shapes.

In this case a rectangle and two triangles.

Now find the area of these smaller shapes.

Add all three areas together to get your answer.

What about Irregular Shapes?

How do you find the area of this shape?

First – Break shape into smaller REGULAR shapes.

In this case five rectangles.

Now find the area of these smaller shapes.

Add all five areas together to get your answer.