#### Answer

$-1$

#### Work Step by Step

$\dfrac {\tan 80-\tan \left( -55\right) }{1+\tan {80}\tan \left( -55\right) }=\tan \left( 80-\left( -55\right) \right) =\tan 135=-1$

Published by
Pearson

ISBN 10:
013421742X

ISBN 13:
978-0-13421-742-0

$-1$

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