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Lesson Example Discussion Quiz: Class Homework

Example

Title: Circumference of a circle

Grade: 8-a Lesson: S4-L3

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

Examples:

Example: 1a

If the radius of the circle is 25 units, find the circumference of the circle.

Radius = 25 units
Circumference of circle formula \$(C)\$= 2πr
C = \$2 × (22/7) × 25\$ = 157 units

Explanation: In the above problem, the radius of the circle is 25 units. By using the formula \$(C)\$= 2πr, we get the circumference of a circle as 157 units.

Example: 2a

Calculate the circumference of the circle whose area is 202 cm².

Area of the circle A = 202 cm²
A = πr²
⇒ 202 = πr²
⇒ r²= 202/π (π = 22/7)
⇒ r² = \$(202 \times 7) / 22\$
⇒ r² = 64
⇒ r = 8 cm
Circumference of the Circle C = 2πr ⇒ C = 2 x (22/7) x 8
⇒ C = 352/7
⇒ C = 50.2cm

Explanation: In the above problem, the area of a circle is 202 cm² and the formula for the circumference of a circle is 2πr. Therefore, the circumference of circle 50.2 cm.

Example: 3a

Calculate the circumference of circle, whose diameter is 10m.

Diameter = 10m.
Hence, radius = \$d/2\$ = \$10/2\$ = 5 m
Circumference of circle = 2πr units
C = 2(22/7)(5) = 31.4m

Explanation: In the above problem, the circumference of circle is 2πr and given diameter is 10m and radius is 5m. Therefore, the circumference of circle is 31.4 m.