Question

The sum of the areas of two circles is 80 square meters. Find the length of a radius of each circle if one of them is twice as long as the other.

Answer 1

The area of a circle is given or expressed as:

A = (pi)r^2

The sum of the areas of two circles is 80 square meters.

A1 + A2 = 80
(pi)r1^2 + (pi)r2^2 = 80

where r1 = 2r2

(pi)2r2^2 + (pi)r2^2 = 80
r2 = 2.91
r1 = 5.83