It's set up like this and you have to solve for all possible angles:(adsbygoogle = window.adsbygoogle || []).push({});

-360 degrees <= theta <= 360 degrees

8cos ^ 2 theta + 7cos theta - 1 = 0

(my work)

(8cos - 1)(cos theta + 1) = 0

8cos theta - 1 = 0

8cos theta = 1

cos theta = 1/8

theta = 1/8 cos ^ -1

theta = 83 degrees

= -83 degrees

= 277 degrees

= -277 degrees

OR

cos theta + 1 = 0

cos theta = -1

theta = -1cos ^ -1

theta = 180 degrees

= -180 degrees

The back of the textbook has only the answers before my "OR", they do not show the possible 180 and -180 degrees that I calculated, did they just forget or did I mess something up?

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# Is this right? (trig equation)

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