f(x)化简为1/2+sin(2x+π/6);在〔-π/2,0〕上,值域[-1/2,1];
向量平行,则对应成比例:x1/x2=y1/y2或x1*y2=x2*y1
cosx/cosx=√3sinx/cosx,求得tgx=√3/3,x=π/6