Question

stabiliti daca a) -3 apartine lui A, unde A={x in Z |0 <2x+1 < 3}​

Answer 1

A = {x ∈ Z | 0 < 2x + 1 < 3}

0 < 2x + 1 < 3       | -1

-1 < 2x < 2            | ÷2

-1/2 < x < 1

$\displaystyle{ -3 \not \in (-\frac{1}{2}, 1) \rightarrow -3 \not \in A}$

q.e.d.