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Reference Angle

Let θ be a non-quadrantalanglein standard position. Itsreference angleis the acute angle α formed by the terminal side of θ and the horizontal axis.

Quadrant I :

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

α = θ

Quadrant II :

α = π θ (radians)

α = 180 ° θ (degrees)

Quadrant III :

α = θ π (radians)

α = θ 180 ° (degrees)

Quadrant IV :

α = 2 π θ (radians)

α = 360 ° θ (degrees)