Question

Determinati elementele multimii A=(xEN/11/(2x+45) si x mai mic ca 40

Answer 1

$2x+45\in\{0,11,22,33,...\}$
$2x\in\mathbb{N}\Rightarrow2x+45\in\{55,66,77,...\}$
$2x\in\{10,21,32,...\}$
$2x~par\Rightarrow2x\in\{10,32,54,...\}$
$x\in{5,16,27,38,49,...\}$
$x<40\Rightarrow x\in\{5,16,27,38\}$
$\boxed{A=\{5,16,27,38\}}$