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Lesson Example Discussion Quiz: Class Homework

Example

Title: Area of a circle

Grade: 8-a Lesson: S4-L4

Explanation: Here are some examples of the topic with images and steps in sequence.

Examples:

Example: 1a

A tin of beans has a diameter of 4 inches.What is the area of the top of the tin?

Diameter = 4 inches
Radius of a circle (r)= \$"diameter"/2\$ = \$4/2\$ =2 inches
Area of a circle = \$πr^2\$
= \$(22/7)\times 2 \times 2\$
= \$88/7\$ = 12.5 sq.inches

Explanation: In the above problem,the given diameter of a tin is 4 inches and the radius is 2 inches. By using the formula \$πr^2\$, the area of the tin is 12.5 sq.inches.

Example: 2a

A circular pond has a radius of 6 yards. Find the area of the pond.

Area of a circle = \$πr^2\$
Given Radius = 6 yards
Area of a pond = \$(22/7) \times 6 \times 6 \$
= \$(22/7) \times 36\$ = \$792/7\$
= 113.14 sq.yards

Explanation: In the above problem, the circular pond has a radius of 6 yards. By using the formula \$πr^2\$, the area of the circular pond is 113.14 sq.yards.

Example: 3a

The circumference of a circle is 22cm. Find its area?

Circumference of a circle = 2πr
Given Circumference = 22cm
22 = 2πr
r = \$(22 \times 7)/(22 \times 2)\$
r = \$7/2\$ = 3.5 cm
Area of a circle = \$πr^2\$
= \$(22/7)\times 3.5 \times 3.5\$
= \$(269.5)/7\$ = \$38.5 (cm)^2\$

Explanation: In the above problem, the circumference of a circle is 22cm and its radius is \$3.5 cm\$. By using the formula \$πr^2\$, the area of the circle is \$38.5 (cm)^2\$