sin2x-cos2x-1
=√2(sin2x×√2/2-cos2x×√2/2)-1
=√2sin(2x-π/4)-1
如果本题有什么不明白可以追问,用到的公式可以写出来吗？还是看不太懂∵sinπ/4=√2/2;cosπ4/=√2/2;∴√2(sin2x×√2/2-cos2x×√2/2)-1=√2(sin2xcosπ/4-cos2xsinπ/4)-1(积化和差公式)=√2sin(2x-π/4)-1公式如下：sin(a-b)=sinacosb-sinbcosa;