Question

Find the circumference of the circle whose area is 25times the area of the circle with radius 7cm.

Answer 1

The Area of a Circle with radius r = πr²
The Area of a Circle with radius7 = π(7)²
The Area of the bigger Circle
= 25 x π(7)²
= π(7² x 5²)
= π(35²)
Let radius of the bigger Circle = R
R² = π(35²)
⇒ radius of the bigger Circle = 35
The Circumference of a Circle with radius r = 2πr
The Circumference of a Circle with radiu 35r
= 2π x 35
= 220cm.