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Trigonometry

Express each of the following in terms of the cosine of another angle between 0 degrees and 180 degrees:

a) cos 20 degrees b) cos 85 degrees c) cos 32 degrees

d) cos 95 degrees e) cos 147 degrees f) cos 106 degrees

My answer:

a) - cos 160 degrees b) - cos 95 degrees c) -cos 148 degrees

d) -cos 85 degrees e) - cos 33 degrees f) - cos 74 degrees

Textbook answer:

a) cos 340 degrees b) cos 275 degrees c) cos 328 degrees

d) cos 265 degrees e) cos 213 degrees f) cos 254 degrees

My question: I do understand that the cosine of 20 degrees and 340 degrees are equal; but why are the answers greater than 180 degrees even though I was instructed to express my answer as the cosine of another angle between 0 degrees and 180 degrees.

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  1. clearly they mistyped the question. Your answers are all correct, and theirs are too, if the want answers between 180 and 360

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    oobleck
  2. thanks oobleck appreciate it

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  3. 30wowowowowwowoowowoowowoowow

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