A right circular cylinder has a volume of . If the height of the cylinder is 5, what is the radius of the cylinder?
3
4.5
9
40
Choice A is correct. The volume of a right circular cylinder with a radius of r is the product of the area of the base, , and the height, h. The volume of the right circular cylinder described is
and its height is 5. If the radius is r, it follows that
. Dividing both sides of this equation by
yields
. Taking the square root of both sides yields
or
. Since r represents the radius, the value must be positive. Therefore, the radius is 3.
Choice B is incorrect and may result from finding that the square of the radius is 9, but then from dividing 9 by 2, rather than taking the square root of 9. Choice C is incorrect. This represents the square of the radius. Choice D is incorrect and may result from solving the equation for
, not r, by dividing by
on both sides and then by subtracting, not dividing, 5 from both sides.