SOLUTION: cos(-x)cos x - sin (-x) sin x

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Question 1027182: cos(-x)cos x - sin (-x) sin x
Answer by ikleyn(52803)   (Show Source): You can put this solution on YOUR website!
.
cos(-x)*cos(x) - sin(-x)*sin(x)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

One way to find its value is

cos(-x)*cos(x) - sin(-x)*sin(x) =  = 1.

(On the way I used  cos(-x) = cos(x)  and  sin(-x) = -sin(x)).



The other way is to use the addition formula of trigonometry for cosines,
which is   = .


When you use it with  = -x  and   = x,  you will get

cos(-x)*cos(x) - sin(-x)*sin(x) = cos((-x) + x) = cos(0) = 1.


Both ways lead to the same result.


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