Trigonometry3.1Reference Angles

Reference angleFor any angle θ in standard position it is the positive acute angle between the terminal side of θ and the x-axis.

Reference angle TheoremA trig function of an angle and its reference angle will differ at most in sign.

ExamplesFind the exact value of cos 495°

Find θ if sin θ = -0.3090 with θ in QIV.

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