[tex]\text{Se consider\u a func\c tia} \ f:[0,+\infty )\rightarrow \mathbb{R}, f(x)=\frac{x}{x+1}+\frac{x+1}{x+2}. \ \text{S\u a se demonstreze c\u a } \ \frac{1}{2}\leq f(x)\leq 2, \ \text{pentru orice} \ x\in [0, +\infty )[/tex]