$\frac{1}{2}$- $\frac{1}{3}$+ $\frac{1}{4}$- $\frac{1}{5}$+...+ $\frac{1}{98}$- $\frac{1}{99}$
Đạt A =(1)
⇒A=$\frac{1}{2}$- $\frac{1}{3}$+ $\frac{1}{4}$- $\frac{1}{5}$+...+ $\frac{1}{98}$- $\frac{1}{99}$
A=$\frac{1}{6}$+ $\frac{1}{20}$+...+ $\frac{1}{98.99}$
A=$\frac{1}{2.3}$+ $\frac{1}{4.5}$+...+ $\frac{1}{98.99}$
A=$\frac{1}{2}$- $\frac{1}{99}$
A= $\frac{97}{198}$
