When a circle has its radius increased by 1 cm, its area increases by 43 cm^2. To the nearest integer, how many centimeters was the radius of the circle before it was increased?
Let r be the original radius
We have that
New area - Old area = 43 cm^2
pi (r + 1)^2 - pi r^2 = 43
pi ( r^2 + 2r + 1) - pi r^2 = 43
r^2 + 2r + 1 - r^2 = 43 / pi
2r + 1 = 43/pi
2r = 43/ pi - 1
r = (43/ pi - 1) / 2 ≈ 6 cm
