In using the Biot-Savart Law for an finite wire, I am having trouble understanding the angles. I have sintheta1-sintheta2, where theta1 is measured from point P to the horizontal wire and from the vertical axis, to the left of point P. Theta 2 is measured to the right of point P. I am ok until there. However, in going from that result to that for an infinite wire, my textbook (Serway and Jewett, Physics for scientists and engineers) says that as x goes to - infinity, theta 1 is (pi/2) and as x goes to positive infinity, theta 2 is (-pi/2). I seem to have those backwards, as theta1 being -pi/2 and theta2 being +pi/2. However, when I do it my way, I get an extra negative sign which should not be there. I am hoping someone can explain to my why theta is pi/2 to the left of point P and -pi/2 to the right of point P.