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A cone has a height of inches and a radius of inches. If a plane cuts the cone inches above the base of the cone, write an expression for the area of the circular cross-section.

Area of a circle

Sketch the radius and look for a geometric way to find its length.

Do you see the similar triangles?

Similar triangles have proportional sides, write a proportion to solve for . Be careful! The height of the small triangle is not .