What is the directrix 9x^2-4 ?

The directrix 9x^2-4 is y=-145/36

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directrix 9x^2-4

directrix

9 x^{2} - 4

y = - \frac{145}{36}

Solution steps

Rewrite

y = 9 x^{2} - 4

in the standard form:

4 \cdot \frac{1}{36} (y - (- 4)) = (x - 0)^{2}

(h, k) = (0, - 4), p = \frac{1}{36}

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

- p

from the center

(0, - 4)

y-coordinate

y = - 4 - p

y = - 4 - \frac{1}{36}

Refine

y = - \frac{145}{36}

- x^{2} + 8 x - 15

y = - (x - 4)^{2} + 1

- 12 y + 10 = x^{2} - 4 x + 14

- 2 x^{2} + 11

y = (x - 4) (x - 7)