证明sin^4x-cos^4x=sin^2x-cos^2x

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证明sin^4x-cos^4x=sin^2x-cos^2x证明sin^4x-cos^4x=sin^2x-cos^2x证明sin^4x-cos^4x=sin^2x-cos^2xsin^4x-cos^4x

证明sin^4x-cos^4x=sin^2x-cos^2x
证明sin^4x-cos^4x=sin^2x-cos^2x

证明sin^4x-cos^4x=sin^2x-cos^2x
sin^4x-cos^4x=(sin^2x-cos^2x )(sin^2x+cos^2x)
=(sin^2x-cos^2x )*1=(sin^2x-cos^2x )

sin^4x-cos^4x
=(sin^2x+cos^2x)(sin^2x-cos^2x)
=(sin^2x-cos^2x)

sin^4x-cos^4x=(sin^2x-cos^2x)(sin^2x+cos^2x)
因为sin^2x+cos^2x=1
所以sin^4x-cos^4x=sin^2x-cos^2x