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Lesson Example Discussion Quiz: Class Homework

Example

Title: Circles

Grade: 8-a Lesson: S4-L2

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

Examples:

Example: 1a

Find the area of a circular region whose radius is 21 mm.

Radius of circular region = r = 21 mm

Area of a circle = πr2

= (22/7) × 21 × 21

= 22 × 3 × 21  = 1386 sq.mm

Explanation: In the above problem, the radius of circular region (r) is 21mm. By using the formula Area of a circle = πr2, the area of the given circular region is 1386 sq.mm.

Example: 2a

A circle has a diameter 142.8 mm. Find its radius.

Diameter of a circle(d) = 142.8 mm
Diameter of a circle (d)= \$2 \times r\$
142.8 = 2 x r
```
r = 142.8 / 2 = 71.4
```
Radius(r) = 71.4 mm

Explanation: In the above problem, a circle has a diameter 142.8 mm. By using Diameter of a circle (d)= \$2 \times r\$, the radius of the circle is 71.4 mm.

Example: 3a

Captain digs a 12-foot wide circular hole in his garden.What is the area of the circular hole?

Radius of a hole = \$12 \div 2 = 6 "feet"\$
Area of a circle = πr2
= \$(22/7) \times 6 \times 6\$
= 113.1 sq.ft

Explanation: In the given problem, the diameter of the circular hole is 12 feet and the radius is 6 feet. By using Area of a circle = πr2, the area of the circular hole is found to be 113.1 sq.ft.