Equation of parabola is
.
Explanation:
The vertex form of the parabola is given as,

where (h,k) is the vertex of the parabola.
If the parabola must be symmetric about x = -10 then the axis of symmetry must be x = -10.
To execute this, h should be -10, and it was plugged in the vertex form of the parabola, a and k may be any real number.
So the equation can be written as,
