cos(-120°), sin(-30°), -sin(150°)
This problem requires you to understand the symmetric identities for the sin and cos functions. sin(-150°) is in the 3rd quadrant and is 30° away from the X axis. Now let's look at all the possibilities:
cos(-120°) - Also in the 3rd quadrant and 30° away from the Y axis. MATCH.
sin(150°) - It's in the 2nd quadrant. Will have opposite sign. Not a match.
sin(-30°) - It's in the 4th quadrant. The signs will match. It's also 30° away from the X axis. MATCH.
-sin(150°) - The identity sin(-a) = -sin(a) applies here. MATCH.
cos(60°) - In 1st quadrant. Result will be positive. Not a match.
cos(-60°) - In 4th quadrant. Result will be positive. Not a match.
