On the unit circle, cosine is the x-coordinate and sine is the y-coordinate. Radius 1, so the point is (cos θ, sin θ). Right-triangle values are in right-triangle trigonometry.
Quadrant signs
Cosine is negative in quadrant II. Sine is negative in quadrant IV. SOHCAHTOA still names the ratios, in SOHCAHTOA. Reference angles bring any θ back to the first quadrant, in reference angles.
The bottom line
(cos θ, sin θ) on the unit circle. Signs come from the quadrant.
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