计算sin^4(3π/8)-cos^4(3π/8)

来源：学生作业帮编辑：神马作文网作业帮分类：数学作业时间：2024/11/13 00:05:28

原式=[sin^2(3π/8)-cos^2(3π/8) ][sin^2(3π/8)+cos^2(3π/8) ] =[sin^2(3π/8)-cos^2(3π/8)] =[sin^2(3π/8)-(1-sin^2(3π/8)} =2sin^2(3π/8)-1 利用二倍角公式可得 =1-cos3π/4-1 =-cos3π/4 =-cos（π-π/4） =cosπ/4 =根号2除以2

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