Answer
$0$
Work Step by Step
We know that $\tan(\theta)=\cot(90^{o}-\theta)$.
Hence,
$\tan(42^{o})-\cot(48^{o})\\
=\cot(90^{o}-42^{o})-\cot(48^{o})\\
=\cot(48^{o})-\cot(48^{o})\\
=0$
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