radius of a cylinder

Question

The volume of a cylinder is 128π cubic inches. If the cylinder's height is 8, what is the radius of the cylinder?

Answer 1

128pi = hpi(r^2) = 8pi(r^2)

r^2 = 128/8pi = 16/pi

r = 4/sqr(pi) inches = the radius

r = 4/sqrpi =about 2.26 inches rounded to 2 decimal places

Answer 2

128 = (1/3)πr²(8)

Solve for r and answer.