Question

Cos(-170°) = _____ -cos10° cos10° cos(-10°)

Answer 1

Answer:

-cos10°

Step-by-step explanation:

cos is positive at first and fourth quadrant

so, cos (-x) = cos (x)

also, cos(180-x) = -cos x

        cos (180+x) = -cos x

cos (-170°) = cos (170°)

cos(170°) = cos (180° - 10°)

              =  - cos 10°