2.3. Find all values of $a$ for which the quadratic function $f(x)=a x^{2}+2 a x-1$ takes values, the modulus of which does not exceed 3, at all points of the interval $[-2 ; 0]$. In your answer, specify the total length of the intervals to which the found values of $a$ belong.
Answer: 6 (the set of desired values of $a$: $[-4 ; 0) \cup(0 ; 2]$).