SOLUTION: How do you express functions in terms of the same function which has a positive acute angle.

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How do you express functions in terms of the same function which has a positive acute angle.
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You need a reference angle,
and you need the sign of
the original function.
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Example:
sin(220 degrees)
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The sign is negative because sin is negative in the 3rd Quadrant.
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The reference angle is the acute angle between the terminal side
of 220 degrees and the closest segment of the x-axis.
That angle is 220-180 = 40 degrees.
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So sin(220) = -sin(40)
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Cheers,
Stan H.