cos(120°-x). 
cos(120°-x). cos［180°-(60°+x)］+2sin(x-60°)=sin(x+60°)+
cos(60°+x)+2sin(x-60°)
=2［
sin(x+60°)+
cos(60°+x)］+2sin(x-60°)
=2［cos60°sin(x+60°)+sin60°cos(60°+x)］+2sin(x-60°)
=2sin(x+120°)+2sin(x-60°)
=2sin(180°-60°+x)+2sin(x-60°)
=-2sin(x-60°)+2sin(x-60°)=0.
点评：
本题运用“异角化同角”思路.