zhangpengfei
春芽
共回答了20个问题采纳率:85% 举报
cosa-sina=3√2/5, cosa=sina+3√2/5 , cos^2a=sin^2a+6√2/5sina+18/25
2sin^2a+6√2/5sina-7/25=0=(√2sina-1/5)(√2sina+7/5) , sina=-7√2/10 , (sina=√2/10舍去)
cosa=-√2/10
sin2a=2sinacosa=2(-√2/10)(-7√2/10)=7/25 , tana=7
tan(π/4+a)=(1+7)/(1-7)=-7/6
1年前
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