F=y^3i-x^3j+z^3k;C the trace of the cylinder x^2+y^2=1 in the plane x+y+z=1 and i arrive at -3integrate 0 to pi/2 integrate 0 to 1 r^4 dr dθ and obtain the answer -3pi/8 but the answer given is -3pi/2.This imply that it integrate from 0 to 2pi.But why this happen since the region is generated from 0 to pi/2 only i think.Thanks.