Find the value of the given tignometric function cos150degre

Find the value of the given tignometric function cos(150degrees)?

Solution

given cos(150) = cos(pi-30)

use cos(A - B) = cos A cos B + sin A sin B

  cos(pi-30) = cospi cos30 - sinpi sin30

= (-1) *sqt3/2 - 0*1/2

= - sqt3/2

cos150 = - sqt3/2