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The Humongous Book of Trigonometry Problems by W. Michael Kelley

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Reference Angles

Shrink rays that turn any angles into acute angles

4.1    Given acute angle θ in the diagram below, draw reference angles in the second, third, and fourth quadrants that have the same measure as θ.

A reference angle is an acute angle formed by a terminal side and the x-axis. Reference angles are not necessary in the first quadrant, but each of the other quadrants requires them. The diagram below illustrates the reference angles for the second, third, and fourth quadrants, each with an angle measure of θ.

Even though the size ...

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