Question

A pyramid with a square base is cut by a plane that is parallel to its base and is 2 units from the base. The surface area of the smaller pyramid that is cut from the top is half the surface area of the original pyramid. What is the altitude of the original pyramid

Answer 1

6.83 units

Explanation:

Let the height of the original pyramid be represented by h. Then the cut off top has a height of (h -2). The scale factor for the area is the square of the scale factor for height, so we have ...

(height ratio)^2 = 1/2

((h -2)/h)^2 = 1/2

(h -2)√2 = h . . . . . . square root; multiply by h√2

h(√2 -1) = 2√2 . . . . add 2√2 -h

h = (2√2)/(√2 -1) ≈ 6.8284 . . . units

The altitude of the original pyramid is about 6.83 units.