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Q 10.

Expert-verifiedFound in: Page 643

Book edition
6th

Author(s)
Sullivan

Pages
1200 pages

ISBN
9780321795465

Answer Problem using the figure.

If *a* = 4, then the equation of the directrix is______ .

If *a* = 4, then the equation of the directrix is

*y* = -2.

We have given *a* = 4 and graph of parabola is,

Directrix of the parabola:

The directrix is **perpendicular to the axis of symmetry of a parabola and does not touch the parabola**.

Formula for the directrix for upward parabola is: y = k - a.

We have given graph is,

This parabola is upward parabola so directrix of the parabola is,

$y=k-a$.

Where " *k* " is the y-coordinate of the vertex.

From figure we have vertex = (3, 2).

So equation for the directrix is,

*y* = 2 - 4 = -2.

If *a* = 4, then the equation of the directrix is *y* = -2.

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