Question

найти cosa если tga=2корень2 и 0<а<п/2

Answer 1

$0\ \textless \ \alpha \ \textless \ \frac{\pi}{2}\\1+tg^2 \alpha =\frac{1}{cos^2 \alpha }\\cos^2 \alpha =\frac{1}{1+tg^2 \alpha }=\frac{1}{1+8}=\frac{1}{9}\\cos \alpha =\frac{1}{3}$