sin(2a+b)/sina -2cos(a+b)
问题描述:
sin(2a+b)/sina -2cos(a+b)
答
原式=(sinacos(a+b)+cosasin(a+b))/sina-2cos(a+b)
=cosasina(a+b)/sina-cos(a+b)
=(cosasina(a+b)-sinacos(a+b))/sina
=sin(a+b-a)/sina
=sinb/sina