sin(2a+β)/sina-2cos(a+β)=sinβ/sina

sin(2a+β)/sina-2cos(a+β)=sinβ/sina
sin(2a+β)/sina-2cos(a+β)=sinβ/sina

sin(2a+β)/sina-2cos(a+β)=sinβ/sina
这问题是求啥啊?证明等式

sin(2a+b)=sin(a+a+b)=sinacos(a+b)+cosasin(a+b)=sinacos(a+b)+cosa(sinacosb+cosasinb) =sinacos(a+b)+sinacosacosb-sinasinasinb+sinasinasinb+cosacosasinb =sinacos(a+b)+sinacos(a+b)+sinb =2sinacos(a+b)+sinb sin(2a+b)-2sinacos(a+b)=sinb sin(2a+b)/sina-2cos(a+b)=sinb/sina