Question

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

Answer 1

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