Trigonometric identity

vvkannan

Joined Aug 9, 2008
138
From the identity
cos(x+y)=cosxcosy-sinxsiny
Now if x=y
cos 2x=cos^2 x - sin ^2 x
cos 2x=cos ^2 x- (1-cos^2 x)
cos 2x=2 cos^2 x - 1
cos ^2 x= (1+cos 2x)/2
 
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