求证sin^4x-cos^4x=sin^2x-cos^2x
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求证sin^4x-cos^4x=sin^2x-cos^2x
求证sin^4x-cos^4x=sin^2x-cos^2x
求证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^4x-cos^4x =(sin^2x+cos^2x)(sin^2x-cos^2x)=(sin^2x-cos^2x)
同一楼
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