#### Answer

$(x-7)(x+3)$

#### Work Step by Step

To factor by trial and error, determine the two numbers that, when multiplied, equal the third term, and, when added, equal the coefficient of the middle term.
$x^2-4x-21$
$=(x-7)(x+3)$

Published by
Brooks Cole

ISBN 10:
0-53449-636-9

ISBN 13:
978-0-53449-636-4

$(x-7)(x+3)$

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