Só sánh: [tex]\frac{7^{18}}{7^{18}+2}[/tex] và [tex]\frac{7^{18}+1}{7^{18}+3}[/tex]
Ta có:
[tex]\frac{7^{18}}{7^{18}+2} \Rightarrow 1 - \frac{7^{18}}{7^{18}+2} = \frac{2}{7^{18}+2}[/tex]
[tex]\frac{7^{18}+1}{7^{18}+3}[/tex] => [tex]1 - \frac{7^{18}+1}{7^{18}+3}=\frac{2}{7^{18}+3}[/tex]
Vì [tex]7^{18}+ 2 < 7^{18}+3 \Rightarrow \frac{2}{7^{18}+ 2} > \frac{2}{7^{18}+3}[/tex]
Vậy ......