The volume of a cylinder is 4 pi x cubed cubic units and its height is x units. Which expression represents the radius of the cylinder, in units?

Use the cylinder volume formula V = πr²h. Substituting V = 4πx³ and h = x gives 4πx³ = πr²x. Divide both sides by πx to get r² = 4x², so the radius is 2x (taking the positive value for a length). The correct choice is 2x.

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