# How do you find the related acute angle?

The related acute is an acute angle ($< {90}^{\circ}$) that can be found between the terminal arm and the x-axis when the terminal arm is in quadrants 2, 3, or 4. There is no related acute angle if the terminal arm lies in quadrant 1.
If the terminal arm is in quadrant 2, do ${180}^{\circ}$ minus the principle angle to find the related acute angle.
If the terminal arm is in quadrant 3, do the principle angle minus ${180}^{\circ}$ to find the related acute angle.
If the terminal arm is in quadrant 4, do ${360}^{\circ}$ minus the principle angle to find the related acute angle.