9-2. Find all positive $a$ for which the equation

$$
\frac{4 \pi a + \arcsin (\sin x) + 3 \arccos (\cos x) - a x}{2 + \tan^2 x} = 0
$$

has exactly three solutions. In your answer, specify the sum of all found $a$ (if such $a$ do not exist, then specify 0; if the number $a$ is not an integer, then round it to the hundredths).
Solution. For $a=1, a=2/3, a=4/5$. The sum is $2.4(6)$.

Answer: 2.47.