What is the directrix y^2=-9x ?

The directrix y^2=-9x is x= 9/4

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directrix y^2=-9x

directrix

y^{2} = - 9 x

x = \frac{9}{4}

Solution steps

Rewrite

y^{2} = - 9 x

in the standard form:

4 (- \frac{9}{4}) (x - 0) = (y - 0)^{2}

(h, k) = (0, 0), p = - \frac{9}{4}

Parabola is symmetric around the x-axis and so the directrix is a line parallel to the y-axis, a distance

- p

from the center

(0, 0)

x-coordinate

x = 0 - p

x = 0 - (- \frac{9}{4})

Refine

x = \frac{9}{4}

9 x^{2} - 16 y^{2} = 144

f (x) = 3 x^{2} - 12 x + 4

16 x^{2} + 9 y^{2} = 144

f (x) = x^{2} - 3 x + 2

f (x) = x^{2} + 3 x - 4