Question

Cos(-170°) = _____

-cos10°
cos10°
cos(-10°)

Answer 1

-cos10°

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°