So sánh: 25/26 và 50/51

* Hướng dẫn giải

$$\begin{gathered} a)Xét1 -\frac{25}{26}=\frac{1}{26};1 -\frac{50}{51}=\frac{1}{51}. \\ Vì \frac{1}{26}>\frac{1}{51}=>\frac{25}{26}<\frac{50}{51} \end{gathered}$$

$$\begin{gathered} b)Xét1 -\frac{213}{321}=\frac{108}{321};1 -\frac{105}{213}=\frac{108}{213}. \\ Vì \frac{108}{321}<\frac{108}{213}=>\frac{213}{321}>\frac{105}{213} \end{gathered}$$

$\begin{array}{l}c)Xét1 +\frac{-99}{100}=\frac{1}{100};1 +\frac{-21}{22}=\frac{1}{22}.\\ \\ Vì \frac{1}{100}<\frac{1}{11}=>\frac{-99}{100}>\frac{-21}{22}\\ \\ d)Xét1 +\frac{-124}{129}=\frac{5}{129};1 +\frac{-132}{137}=\frac{5}{137}. \\ \\ Vì \frac{5}{129}>\frac{5}{137}=>\frac{-124}{129}>\frac{-132}{137}\end{array}$