化简 (21 21:8:15)sin(2a+b)/sina-2cos(a+b)

问题描述:

化简 (21 21:8:15)
sin(2a+b)/sina-2cos(a+b)

sin(2a+b)/sina-2cos(a+b)=[sin(2a+b)-2cos(a+b)sina]/sina =[sina*cos(a+b)+sin(a+b)*cosa-2cos(a+b)sina]/sina =[sin(a+b)*cosa-cos(a+b)sina]/sina =sin(a+b-a)/sina=sinb/sina