求角A
1+tanA/tanB
=1+(sinAcosB)/(cosAsinB)
=(sinAcosB+cosAsinB)/(cosAsinB)
=sin(A+B)/(cosAsinB)
=sinC/(cosAsinB)
再由正弦定理:
sinC/sinB = c/b,
∴sinC/(cosAsinB)=-2sinC/sinB
1/cosA =-2,
cosA = -1/2,
A = 120°
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=1+(sinAcosB)/(cosAsinB)
=(sinAcosB+cosAsinB)/(cosAsinB)
=sin(A+B)/(cosAsinB)
=sinC/(cosAsinB)
再由正弦定理:
sinC/sinB = c/b,
∴sinC/(cosAsinB)=-2sinC/sinB
1/cosA =-2,
cosA = -1/2,
A = 120°
如果你认可我的回答,请点击“采纳为满意答案”,祝学习进步!
手机提问的朋友在客户端右上角评价点【满意】即可
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