Question

what is this (θ+360) % 360, where % is modulo.

Answer 1

\(\theta\) is an angle. Adding 360 degrees to an angle will add a complete revolution to that angle, giving an "identical" angle:

The "modulo" means to say that the angles are congruent, even though they're technically not the same.

It's like the hours on a clock: 1 PM and 1 AM use the same number, but they are not the same time of they. It's the same hour because the 1 repeats every 12 hours.