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问题: △ABC

在△ABC中,SinA=3/5,SinC+CosC<0,a=3√3,b=5,求边C

解答:

∵ a/sinA=b/sinB,∴ sinB=√3/3,c/sin(A+B)=a/sinA,
∴ c=asin(A+B)/sinA…(*), sinC+cosC<0, ∴ π/2<C<π, ∴ A,B均为锐角.
sin(A+B)=sinAcosB+cosAsinB=(3/5)×(√6/3)+(4/5)×(√3/3)=(3√6+4√3)/15, 把它代入(*)式,得c=(3√6+4√3)/9