高中三角函数计算题求解.

cosx+cos(x-π/3)
=cos(x-π/6+π/6)+cos(x-π/6-π/6)
=cos(x-π/6)cos(π/6)-sin(x-π/6)sin(π/6)+cos(x-π/6)cos(π/6)+sin(x-π/6)sin(π/6)
=2cos(x-π/6)cos(π/6)
=2(-(根号3)/3)*(根号3)/2
=-1
选c
哎,没分,白打了那么久