I have a physics problem that states
|| What is the magnetic field at the position of the dot in Figure ex $32.5$ ? Give your answer as a vector.
The correct solution is (according to the book) using The Biot-Savart law,
My question is why is the book choosing to use $\sin(135^\circ)$ ? I understand this has something to do with perspective and convention. My assumption is convention would say the angle of theta starts from the positive $x$ axis. I want to understand why this solution uses the angle of theta from what appears the negative $x$ axis. As $\sin(135^\circ)$ is noted from WolframAlpha below.