2. Given the function $f(x)=a x^{2}-c$, satisfying $-4 \leqslant f(1) \leqslant-1,-1 \leqslant f(2) \leqslant 5, f(3)$'s range of values is $\qquad$ .
2. $-1 \leqslant f(3) \leqslant 20$.

Let $f(3)=m f(1)+n f(2)$, i.e., $9a-c=m(a-c)+n(4a-c), a, c$ have corresponding coefficients respectively $\frac{8}{3} f(2) \leqslant 20$.