SOLUTION: Please can you help me wit equation: calculate exact value of: cos 105°

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Question 974366: Please can you help me wit equation: calculate exact value of: cos 105°
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
cos (60+45) would work
cos(60)*cos(45)-sin(60)sin(45)
(1/2)*(sqrt(2)/2)-(sqrt(3)/2)*sqrt(2)/2
[sqrt(2)/4]-sqrt(6)/4=
(1/4) (sqrt(2)-sqrt(6))
(1/4)(-1.0352)
=-0.2588