What is the directrix 20y=(x-12)^2-20 ?

The directrix 20y=(x-12)^2-20 is y=-6

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directrix 20y=(x-12)^2-20

directrix

20 y = (x - 12)^{2} - 20

y = - 6

Solution steps

Rewrite

20 y = (x - 12)^{2} - 20

in the standard form:

4 \cdot 5 (y - (- 1)) = (x - 12)^{2}

(h, k) = (12, - 1), p = 5

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

(12, - 1)

y-coordinate

y = - 1 - p

y = - 1 - 5

Refine

y = - 6

- 3 x^{2}

x^{2} - 8 x + 24

y = (x - 1)^{2} + 3

+ y = x^{2} + 2 x - 3

8 - 3 x - 2 x^{2}