What is the directrix 13+4x-x^2 ?

The directrix 13+4x-x^2 is y= 69/4

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directrix 13+4x-x^2

directrix

y = \frac{69}{4}

Solution steps

Rewrite

y = 13 + 4 x - x^{2}

in the standard form

4 (- \frac{1}{4}) (y - 17) = (x - 2)^{2}

(h, k) = (2, 17), 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

(2, 17)

y-coordinate

y = 17 - p

y = 17 - (- \frac{1}{4})

Refine

y = \frac{69}{4}