漫舞人生
幼苗
共回答了20个问题采纳率:100% 举报
cos^8x-sin^8x+1/4sin2x sin4x
=(cos^4x+sin^4x)(cos^4x-sin^4x)+1/2sin^22xcos2x
=(cos^4x+sin^4x)(cos^2x-sin^2x)+2sin^2xcos^2x(cos^2x-sin^2x)
=cos^6x-sin^6x+sin^2xcos^4x-sin^4xcos^2x
=cos^4x-sin^4x
=cos^2x-sin^2x
=cos2x
不懂追问
1年前
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