snowsue
春芽
共回答了21个问题采纳率:90.5% 举报
sin(-1071°)=sin(-360*3+9)=sin9
sin99°=cos(90-99)=cos9
sin(-171°)=sin(-180+9)=-sin9
sin(-261°)=sin(-360+99)=sin99=cos9
原式=sin9cos9-sin9cos9=0
sin(α-2π)=sinα
sin(π-α)=sinα
1+sin(α-2π)×sin(π-α)-2cos^2(-α)
=1+sin^2(α)-2cos^2(α)
=1+(1-cos2α)/2-(1+cos2α)
=1/2-3/2cos2α
1年前
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