Question

The directrix of the parabola -40x = y2 is:

Answer 1

The directrix of parabola
`y^2 = -40x` is the line x = +10.

Explanation:

The general form of parabola is given as
`y^2 = 4px`

where the directrix is the vertical line x = - p .

If p > 0, then parabola opens to the right.

If p < 0 then parabola opens to the left.

Now here, the given equation is
`y^2 = -40x`

Representing the given equation in standard form:

`y^2 = 4(-10) x`

⇒ p = -10

So, the directrix of the parabola is x = - p = - (-10) = 10

or, x = + 10

Hence, the directrix of parabola
`y^2 = -40x` is the line x = +10.