Other angles in cosine curve

[RunnerKidElectronic]

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.

 

[Harry_the_cat]

Looks like the textbook hasn't limited the angle to one between 0 and 180. Obviously an error in the wording of the question if those are the expected answers..

 

[Otis]

Hi RKE. Your answers are correct, for the exercise as worded. Looks like a book error. Maybe someone was thinking about the second half of the period but designated the first half instead. Or, the question measurements got swapped with the answer measurements at the print shop. Or, a graduate student who got talked into writing the answer section for the professor's book misread the question. Or...

?

 

[RunnerKidElectronic]

Thanks Harry and Otis. Really appreciate what you guys do here.