Trigonometry · Intermediate · 5 min
Reference angles
A reference triangle separates the size of a trigonometric value from its sign.
WHAT HAPPENS IF…What is the reference angle for 140°?
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Reflect the unit-circle point into the first quadrant. Its coordinate magnitudes are cosα and sinα. The original quadrant determines the signs. On an axis, the limiting reference angle is 0° or 90°; there is no nondegenerate reference triangle there.
A detail that matters
Using the reference angle alone loses the sign information.
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