Answer
$\tan 72^{0}$
Work Step by Step
$\alpha +\beta =\dfrac {\pi }{2}\Rightarrow \tan \alpha =\cot \beta \Rightarrow 72^{0}+18^{0}=\dfrac {\pi }{2}\Rightarrow \cot 18^{0}=\tan 72^{0}$
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