Question

The value of $\frac{1-{\tan }^2{15}^o}{1+{\tan }^2{15}^o}=$ __

Answer 1

Apply the formula,

$\frac{1-ta{n}^{2}A}{1+ta{n}^{2}A}=\cos 2A$

therefore,

$\frac{1-ta{n}^2{15}^{\circ }}{1+ta{n}^2{15}^{\circ }}=\cos {30}^{\circ }$

$=\frac{\sqrt{3}}{2}$