What is the directrix-0.4x^2-5 ?

The directrix-0.4x^2-5 is y=-4.375

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directrix-0.4x^2-5

directrix

y = - 4.375

Solution steps

Rewrite

y = - 0.4 x^{2} - 5

in the standard form:

4 (- 0.625) (y - (- 5)) = (x - 0)^{2}

(h, k) = (0, - 5), p = - 0.625

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, - 5)

y-coordinate

y = - 5 - p

y = - 5 - (- 0.625)

Refine

y = - 4.375