Question

Найдите tg в квадрате альфа, если cos в квадрате альфа=5/13

Answer 1

$\cos^2\alpha+\sin^2\alpha=1\mid\div\cos^2\alpha\medskip\\1+\mathrm{tg}^2\alpha=\dfrac{1}{\cos^2\alpha}\medskip\\\mathrm{tg}^2\alpha=\dfrac{1}{\cos^2\alpha}-1\medskip\\\cos^2\alpha=\dfrac{5}{13}\Rightarrow\mathrm{tg}^2\alpha=\dfrac{1}{\frac{5}{13}}-1=\dfrac{13}{5}-\dfrac{5}{5}=\dfrac{8}{5}$

Ответ. $\mathrm{tg}^2\alpha=\dfrac{8}{5}$