Найти tg^2, если 5sin^2a+13cos^2a=6

Tg^2 (a) = sin^2 (a) / cos^2 (a)

6 = 6sin^2 (a) + 6cos^2 (a) - основное тригонометрическое тождество

5sin^2 (a) + 13cos^2 (a) - 6sin^2 (a) - 6cos^2 (a) = 0

7cos^2 (a) = sin^2 (a)

tg^2 (a) = 7