lean_workbook_plus_40069

Prove that\n(a) if $y=\frac{x^{2}+x+1}{x^{2}+1}$ , then $\frac{1}{2} \leq y \leq \frac{3}{2}$ ,\n(b) if $y= \frac{x^{2}+1}{x^{2}+x+1}$ , then $\frac{2}{3} \leq y \leq 2$ .