Suppose the graph of y=f(x) includes the points (1,5), (2,3), and (3,1). Based only on this information, there are two points that must be on the graph of y=f(f(x)). If we call those points (a,b) and (c,d), what is ab+cd?
ab + cd = (-11)(7) + (2)(3) = -71.
