Question #3fa40

1 Answer
salamat
May 18, 2017

see below

Explanation:

#cos^2 X - sin^2 X = 2 cos^2 X -1#

we use LHS to prove RHS
we know that,
#sin^2 X + cos^2 X = 1#, then
#sin^2 X = 1 - cos^2 X#

therefore
#cos^2 X - sin^2 X = cos^2 X - (1 - cos^2 X)#

#cos^2 X - sin^2 X = cos^2 X -1 +cos^2 X #

#cos^2 X - sin^2 X = 2cos^2 X -1# -->proved

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