Let (P,r) denote a circle with center P and radiusr. Circles (A,a) and (B,b) are externally tangent withaless thanb. Let CD and EF be the common external tangents to circles (A,a) and (B,b) with C and F on circle (A,a) and D and E on circle (B,b). What is the area of trapezoid CDEF in terms ofaandb?