What is the directrix y=-0.005x^2+x+5 ?

The directrix y=-0.005x^2+x+5 is y=105

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directrix y=-0.005x^2+x+5

directrix

y = - 0.005 x^{2} + x + 5

y = 105

Solution steps

Rewrite

y = - 0.005 x^{2} + x + 5

in the standard form

4 (- 50) (y - 55) = (x - 100)^{2}

(h, k) = (100, 55), p = - 50

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

(100, 55)

y-coordinate

y = 55 - p

y = 55 - (- 50)

Refine

y = 105

y = x^{2} - 9 x + 3

- 2 x^{2} - 24 x - 54

x^{2} - 2 x - 3

y = (3 x - 7)^{2}

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