Find the work done by the Force Field F to make a displacement on the curve C. F= <-y^2 , x> C: semicircle x^2 + y^2 = 1 , y<=0 , from (-1,0) to (1,0) since y<=0 , then it's the semi circle under the x-axis. and according to the solution I have: Work=integral[sin t - sin t cos^2 t +(1+cos 2t)/2] dt form t= -pi to t=0 Now I understand everything going on except the limits. why from -pi to 0? why not from pi to 2pi? And it may not make a difference here, but if the integral had a constant inside it would.