2cos方¤/2=cos¤+1
f(x)=2sinx*cos方¤/2+cosx*sin¤
=sinx*cos¤+cosx*sin¤+sinx
=sin(x+¤)+sinx
=2sin(x+¤/2)cos¤/2
=2sin(π+¤/2)cos¤/2
=-2sin¤/2cos¤/2
=-sin¤ ,¤=π/2