f(x) be a non -negative continous function such that the area bounded by the curve y=f(x),x-axis and the ordinates x=pi/4 and x=k.pi/4 is
[k sink + pi/4 cosk +21/2k],then f(pi/4) is
This is easy.Just DIFFERENTIATE both sides w.r.t to k and then finally put k=1.