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In two or more complete sentences, use your knowledge of the unit circle to describe why the following trigonometric equation is true.

tan(-20 degrees) = -tan(20 degrees)

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You have to describe why
\tan (-20^(\circ))=-\tan 20^(\circ).

Consider the left side
\tan (-20^(\circ)). Angle
-20^(\circ) is placed at IVth quadrant and has (see attached diagram for signs of cosines - first sign in brackets and sines - second sign in brackets)


\cos (-20^(\circ))=\cos (20^(\circ)),\\\sin (-20^(\circ))=-\sin (20^(\circ)).

Then


\tan (-20^(\circ))=(\sin(-20^(\circ)))/(\cos(-20^(\circ)))=(-\sin(20^(\circ)))/(\cos(20^(\circ)))=-\tan 20^(\circ).

In two or more complete sentences, use your knowledge of the unit circle to describe-example-1
User Dmck
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