A reference angle is the acute angle to the x-axis. Sine, cosine, and tangent use that acute value, then pick a sign from the quadrant. 150° has reference 30°. Trig values to memorize are in trig values to memorize.
Acute first, sign second
Quadrant II: 180° − θ. Quadrant III: θ − 180°. Quadrant IV: 360° − θ. Amplitude and period describe the whole wave, in amplitude and period.
Right-triangle setup is in right-triangle trigonometry. The short list is in ACT Math formulas.
The bottom line
Reduce to an acute angle, then attach the quadrant sign.
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