化简cos^4 a-sin^4 a+2sin^2 a=

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化简cos^4 a-sin^4 a+2sin^2 a=

cos^4 a-sin^4 a+2sin^2 a
=(cos²a+sin²a)(cos²a-sin²a)+2sin²a
=cos²a-sin²a+2sin²a
=cos²a+sin²a
=1

原式=(cos²a+sin²a)(cos²a-sin²a)+2sin²a
=cos²a-sin²a+2sin²a
=cos²a+sin²a
=1

cos^4 a-sin^4 a+2sin^2 a=(cos^2 a-sin^2 a)(cos^2 a+sin^2 a)+2sin^2 a
=cos^2 a-sin^2 a+2sin^2 a=cos^2 a+sin^2 a=1

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