sinA=tanB 切割化弦 得sinAcosB=sinB
又a/sinA=b/sinB得a/b=sinA/sinB,
a=b(1+cosA)得a/b=1+cosA
则sinA/sinB=1+cosA
sinA=sinB+sinBcosA
=sinAcosB+sinBcosA
=sin(A+B)
=sinC
so正弦定理A=C
sinA=tanB 切割化弦 得sinAcosB=sinB
又a/sinA=b/sinB得a/b=sinA/sinB,
a=b(1+cosA)得a/b=1+cosA
则sinA/sinB=1+cosA
sinA=sinB+sinBcosA
=sinAcosB+sinBcosA
=sin(A+B)
=sinC
so正弦定理A=C