What is the directrix y=+x^2-18x+73 ?

The directrix y=+x^2-18x+73 is y=-33/4

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directrix y=+x^2-18x+73

directrix

y = + x^{2} - 18 x + 73

y = - \frac{33}{4}

Solution steps

Rewrite

y = x^{2} - 18 x + 73

in the standard form

4 \cdot \frac{1}{4} (y - (- 8)) = (x - 9)^{2}

(h, k) = (9, - 8), p = \frac{1}{4}

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

(9, - 8)

y-coordinate

y = - 8 - p

y = - 8 - \frac{1}{4}

Refine

y = - \frac{33}{4}

y = x^{2} + 4 x + 3

3 x^{2} + 5 x - 4

y = - x^{2} - 1

+ 6 x^{2} + 6 x - 12

y^{2} = 20 (x - 10)