已知cos(x-派/6)=-根号3/3,则cosx+cos(x-派/3)的值是

已知cos(x-派/6)=-根号3/3,则cosx+cos(x-派/3)的值是

cosx+cos(x-派/3)
=2cos(2x-π/3)/2cos(x-x+π/3)/2
=2cos(x-π/6)×cosπ/6
=2×（-√3/3）×√3/2
=-1