Asked by runner
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.
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.