a) $A =\left\{1;2;3;6\right\}$
$B =\left\{2;3;5;7\right\}$
b) $C =\left\{x \in \Bbb R\vert\, 1 < x -1 \leq 4\right\}$
$\to C =\left\{x \in\Bbb R\vert\, 2< x \leq 5\right\}$
Hình bên dưới
c) $A\cap B =\left\{2;3\right\}$
$A\cup B =\left\{1;2;3;5;6;7\right\}$
$A\backslash B =\left\{1;6\right\}$
$B\backslash A =\left\{5;7\right\}$
$A\cap C = \left\{3\right\}$
$B\backslash C =\left\{2;7\right\}$