/sci/ - Science & Math

Using Biot-Savart Law, how do I find the angles for (ui/4piD)(costheta1-costheta2)?

I’ve divided the wires into 3 segments. I know that the first angle should be what comes first in the direction of the current, so my first angle would be 90degrees. But why is the second angle 135 and not 45?
For the 3rd segment, should my first angle be 45 and second angle be 135?
These angles make sense because I end up with a non-negative answer, but I don’t know why they should be 135 instead of 45