Question

Which expression is equivalent to cos120°?

cosine 60 degrees°
cos240°
cos300°
cos420°

Answer 1

cos120°=-5
cos240°=-5

Answer 2

The correct answer for the given question is option b) cos 240 degrees.

This means that the expression cos 120 degrees can also be written as cos 240 degrees.

This because cos 240 degrees = -1/2 = cos 120 degrees.

This happens because the second and third quadrants carry the same signs.