Question

Найдите tg²a если 3sin²a+8cos²a=7

Answer 1

$3sin^2a+8cos^2a=7 \ 3+5cos^2a=7 \ 5cos^2a=4 \ cos^2a= dfrac{4}{5} \ \ tg^2a+1= dfrac{1}{ frac{4}{5} } \ tg^2a= dfrac{5}{4}-1= dfrac{1}{4}$