cosA-acosB=c-a
2R(sinBcosA-cosBsinA)=2R(sinC-sinA)
sinBcosA-cosBsinA=sin(B+A)-sinA
sinBcosA--cosBsinA=sinBcosA+cosBsinA-sinA
2 cosBsinA=sinA
2cosB=1
cosB=1/2
B=30
cosA-acosB=c-a
2R(sinBcosA-cosBsinA)=2R(sinC-sinA)
sinBcosA-cosBsinA=sin(B+A)-sinA
sinBcosA--cosBsinA=sinBcosA+cosBsinA-sinA
2 cosBsinA=sinA
2cosB=1
cosB=1/2
B=30