Grain pouring from a chute at a rate of 60 cubic feet per minute forms a conical pile whose height is always three times that of the diameter. How fast is the height of the
pile increasing at the instant when the pile is 20 feet high?

Given: ae ≅ ce ; de ≅ be prove: abcd is a parallelogram. we have that ab || dc. by a similar argument used to prove that △aeb ≅ △ced, we can show that △ ≅ △ceb by. so, ∠cad ≅ ∠ by cpctc. therefore, ad || bc by the converse of the theorem. since both pair of opposite sides are parallel, quadrilateral abcd is a parallelogram.