Question

How do you do #9? Ignore the rest of the problems

Answer 1

Explanation:

cos (105) = cos( 60 + 45) = cos 60 cos 45 - sin60 sin45

= 1/2 * sqrt (2) /2 - sqrt(3)/2 * sqrt (2)/2

= sqrt (2)/4 - sqrt(6)/4

= 1/4 (sqrt(2) - sqrt (6) )