Question
The value of $\tan 9^{\circ}-\tan 27^{\circ}-\tan 63^{\circ}+\tan 81^{\circ}$ is(a) 2(b) 3(c) 4(d) 0
Step 1
We can use the property that $\tan(90 - \theta) = \cot(\theta)$ to rewrite $\tan 81^{\circ}$ as $\cot 9^{\circ}$ and $\tan 63^{\circ}$ as $\cot 27^{\circ}$. Show more…
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$$ \tan 9^{\circ}-\tan 27^{\circ}-\tan 63^{\circ}+\tan 81^{\circ}=4 $$
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