Question

The radius of a circle is increased by 3 in., which increases the area by 100 in. Find the radius of the original circle. Round to the nearest hundredth.

Answer 1

3.81 inches

Explanation:

πr² + 100 = π(r+3)²

divide by π and simplify:

r² + (100/π) = r² + 6r + 9

100/π = r² + 6r + 9

31.8309886184 - 9 = r² +6r

r² = 6r - 22.8309886184

0 = 6r - 22.8309886184

22.8309886184 = 6r

divide by 6:

3.80516476973 ≈ 3.81 inches