Recently I have started studying imaginary numbers. I've come at the division of complex numbers in polar form. However when I do the exercise I get almost exactly the same answer as in my textbook except in the textbook they switch the signs for reasons I don't quite understand.
The following image is the example from the textbook image
division of z1 and z2
$$ z_1= \frac12 \cos(3\pi / 4)+ i \sin(3\pi/4) $$ $$ z_2 =4 \cos(11\pi / 6)+ i \sin(11π/6) $$
At the last step of the example the signs are switched but I don't understand why. Why do they do that?