#### Answer

$x=-1$

#### Work Step by Step

If the slope is undefined, the line is vertical
(parallel to the y-axis).
The equation of such lines is of the form
$x=a$
If it passes through $(-1, 4),$
$x=-1$

Published by
Pearson

ISBN 10:
0321749006

ISBN 13:
978-0-32174-900-0

$x=-1$

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