$a)f\left(x\right)=\{\begin{array}{l}{x}^2\text{dla}x\in \left[-2,2\right]\\ 1\text{dla}x\in \left(2,4\right]\end{array}$  

$\text{Dla}x\in D_f-2\le x\le 2\vee 2<x\le 4$

A więc:

$x\in D_g-2\le 2x\le 2\vee 2<2x\le 4$   

$x\in D_g-1\le x\le 1\vee 1<x\le 2$