Question

решить уравнение как можно быстрее, пожалуйста

Answer 1

$\sf\displaystyle \frac{\cos^4\alpha-\sin^4\alpha}{\cos^2\alpha}+\frac{2\sin^2\alpha}{\cos^2\alpha}=\frac{1}{\cos^2\alpha}\\\\ \frac{(\cos^2\alpha-\sin^2\alpha)(\cos^2\alpha+\sin^2\alpha)+2\sin^2\alpha}{\cos^2\alpha}=\frac{1}{\cos^2\alpha}\\\\ \frac{\cos^2\alpha-\sin^2\alpha+2\sin^2\alpha}{\cos^2\alpha}=\frac{1}{\cos^2\alpha}\\\\ \frac{\cos^2\alpha+\sin^2\alpha}{\cos^2\alpha}=\frac{1}{\cos^2\alpha}\\\\ \frac{1}{\cos^2\alpha}=\frac{1}{\cos^2\alpha}$

ч.т.д