A frustum of a pyramid is a part of the pyramid with two parallel bases. The lateral faces of the frustum are trapezoids. Use the area formula for a trapezoid to derive a formula for the lateral area of a frustum of a regular square pyramid with base edge lengths b and b and slant height/. b2 5 b 2 A 2(b+b2)l (b+b2)h B 4- 2 C 2(b+62) (b+b) 21