Examples

• In [latex]\mathbb{N}[/latex], the solution set of the equation x + 9 = 15 is {6}.
• In [latex]\mathbb{N}[/latex], the solution set of the inequality x + 9 ≤ 15 is {0, 1, 2, 3, 4, 5, 6}.
• In [latex]\mathbb{R}[/latex], the solution set of the inequality x + 9 ≤ 15 is {x ∈ [latex]\mathbb{R}[/latex] | x ≤ 6} or ] –∞, 6].
• In [latex]\mathbb{R}[/latex], the solution set of the inequality 3x ≥ 15 is {x ∈ [latex]\mathbb{R}[/latex] | x ≥ 3} or [3, –∞[.