cos^4X-sin^4X=2cosX
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Explanation:
We use the following identities
a2n−b2n=(an+bn)(an−bn)
sin2x+cos2x=1
cos(a+b)
=cosacosb−sinasinb
Proof
cos4x−sin4x=(cos2x+sin2x)(cos2−sin2x)
=cos2x−sin2x=cosxcosx−sinxsinx =cos(x+x)=cos2x
it is also well answer it helped me a lot 2
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