What is the equation of the directrix of the parabola given by the equation (y - 3) 2 = 8 (x - 5) ? a. y = 3 b. x = 3 c. x = 5 d. y = - 5

Find the focus and directrix of the parabola with the given equation. Then graph the parabola.

y^=-12x

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y^2=-12x

This is an equation of a parabola with a horizontal axis of symmetry.

Its standard form: (y-k) ^2=4p (x-h), with (h, k) being the (x, y) coordinates of the vertex.

For given equation:

Vertex (0,0)

4p=12

p=3

Focus: (-3,0)

Directrix: x=3

see the graph below as a visual check on the answers:

...

y=± (-12x) ^.5