[tex](a+\frac{1}{a})^{2}+(b+\frac{1}{b})^{2} \geq \frac{1}{2}(a+\frac{1}{a}+b+\frac{1}{b})^{2} \geq \frac{1}{2}(1+\frac{4}{a+b})^{2} =\frac{1}{2}.25=\frac{25}{2}[/tex] Dấu =" xảy ra khi a=b=1/2
