Reference Angle

Quadrant $\text{I}$:

  The given angle and the reference angle are the same angle.

                                $\alpha =\theta$

           

Quadrant $\text{II}$:

                               $\alpha =\pi -\theta$(radians)

                               $\alpha =180°-\theta$(degrees)

           

Quadrant $\text{III}$:

                               $\alpha =\theta -\pi$(radians)

                                $\alpha =\theta -180°$(degrees)

           

Quadrant $\text{IV}$:

                                 $\alpha =2\pi -\theta$(radians)

                                 $\alpha =360°-\theta$(degrees)