Question 135662
For a function of the form {{{f(x)=ax^2+bx+c}}}, the line of symmetry is the  vertical line passing through the vertex.  The x-coordinate of the vertex is given by {{{(-b)/2a}}}, so the equation of the line of symmetry is {{{x=(-b)/2a}}}


For your equation:  {{{a=-2}}} and {{{b=11}}}.


You should be able to take it from here.