Sin(x+π/6)=-13/14;3π/2cos²(x+π/6)=1-sin²(x+π/6)=1-169/196=27/196
cos(x+π/6)=-3√3/14
cosx*cosπ/6-sinx*sinπ/6=3√3/14
√3/2cosx-1/2sinx=3√3/14
sinx*cosπ/6+cosx*sinπ/6=-13/14
√3/2sinx+1/2cosx=-13/14
√3/2*(√3cosx-3√3/7)+1/2cosx=-13/14
3cosx-27/7+cosx=-13/7
4cosx=27/7-13/7
4cosx=14/7
cosx=2/4
cosx=1/2