Prove \(\displaystyle{4}{\sin{{\left({2}\frac{\pi}{{5}}\right)}}}+{\tan{{\left({2}\frac{\pi}{{5}}\right)}}}={5}{\cot{{\left(\frac{\pi}{{5}}\right)}}}\) Attempt: Let the side length be

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$$\left[\begin{array}{cccc}1& 3& 0& -4\\ 2& 6& 0& -8\end{array}\right]$$

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Whether f is a function from Z to R if 
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b) ${\displaystyle f\left(n\right)=\sqrt{n^2+1}}$. 
c) ${\displaystyle f\left(n\right)=\frac{1}{n^2-4}}$.

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The solution set of $\tan <!--\; \; -->\mathrm{\theta <!--\; \theta \; -->}=3\cot <!--\; \; -->\mathrm{\theta <!--\; \theta \; -->}$ is

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