Answer
$=\dfrac {1}{2}\tan 102$
Work Step by Step
$\dfrac {2\tan \alpha }{1-\tan ^{2}\alpha }=\tan 2\alpha \Rightarrow \dfrac {tun51}{1-\tan ^{2}51}=\dfrac {1}{2}\dfrac {2\tan 51}{1-\tan ^{2}51}=\dfrac {1}{2}\tan 102$
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