Найдите значение выражения

Решите задачу:

$5+6tg^2x \cdot (sin^2x+acos^2x) = 7\\\\ 5+6 \frac{sin^2x}{cos^2x} \cdot (sin^2x+a(1-sin^2x)) = 7\\\\ 5+6 \frac{sin^2x}{1-sin^2x} \cdot (sin^2x+a(1-sin^2x)) = 7\\\\ sinx=0.5 \rightarrow \\\\ 5+6 \frac{0.5^2}{1-0.5^2} \cdot (0.5^2+a(1-0.5^2)) = 7\\\\$

$\frac{1.5}{0.75} \cdot (0.25+0.75a) = 7-5\\ 2 \cdot (0.25+0.75a) = 2\\ 0.25+0.75a = 1\\ 0.75a = 1-0.25\\ 0.75a = 0.75\\ a=1$