How to define range of angle within ongoing calculation?

Good day,

i'm trying to work on inverse kinematics on a 5 DOF robotic arm (revolute joints).

But while calculating Theta1- Theta5, how do I apply limitations/range of angles to my code? I looked it up, but the solutions stated, as using linspace or a loop, didn't work. I basically want to limit every angle in the range between -90 and +90 degrees.

Thanks