Reference angle is the smallest angle that the terminal side of a given angle makes with the x-axis. It is positive and always lies between 0 and 90 degrees (Acute angle). Reference angle can be in any of the four quadrants. When determining the reference angle, vertically drop (raise) the line to the horizontal axis (x-axis). Angles in first quadrant are their own reference angles. The angle is measured by the amount of rotation from the initial side to the terminal side.

## Reference Angle Formula

Let $\theta$ be the given reference angle. Given below is the table to find reference angle in different quadrants:

 Quadrant I $\theta$ Quadrant II 180$^{\circ}$ - $\theta$ Quadrant III $\theta$ - 180$^{\circ}$ Quadrant IV 360$^{\circ}$ - $\theta$

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