Nilai dari tan² (π / 14) + tan² (3π / 14) + tan² (5π / 14) adalah ...

[tex]$\begin{align} \sum_{k=1,3,5}\tan^2\left(\frac{k\pi}{14}\right)&= \sum_{k=1,3,5}\frac{\sin^2(\frac{k\pi}{14})}{\cos^2(\frac{k\pi}{14})} \\ &=\sum_{k=1,3,5} \left(\frac{1}{\cos^2(\frac{k\pi}{14})}-1\right) \end{align}[/tex]

[tex]$\begin{align}T_7&=64x^7-112x^5+56x^3-7x \\ &=x(64x^6-112x^4+56x^2-7)\end{align}[/tex]

56/7 = 8
8 - 3(1) = 5

Jadi, jumlah persamaan di atas adalah 5