Question

What is the line symmetry?

Answer 1

The line of symmetry is vertical line that passes through the vertex.

Find vertex of this parabola has x-coordinate:

`x_v=-(b)/(2a).`

Thus,

`x_v=-(8)/(2a)=-(4)/(a).`

Then the line of symmetry has the equation

`x=-(4)/(a)`

and coincides with the line
`x=4.` This means that

`-(4)/(a)=4,\\ \\a=-1.`

Answer: correct choice is B