1、sin（2x+B）/sinx - 2cos（x+B）=sinB/sinx

1.左边=[sinx*cos(x+b)+cosx*sin(x+b)]/sinx-2cos(x+b)
=cos(x+b)+[cosx*sin(x+b)]/sinx-2cos(x+b)
=[cosx*sin(x+b)]/sinx-cos(x+b)
=[cosx*sin(x+b)-2sinx*cos(x+b)]/sinx
={sin[(x+b)-x}/sinx
=sinb/sinx=右边.
2.左边=（sinx+sinB）^2 + （cosx+cosB）^2
=(sinx)^2+2sinx*sinb+(sinb)^2+(cosx)^2+2cosx*cosb+(cosb)^2
=2+2cos(x-b)
=4{cos[(x-B)/2 ]}^2=右边.