C= `2/(1.3)` + `2/(3.5)` + `2/(5.7)` +...+ `2/(97.99)`
C= 1 - `1/3` + `1/3` - `1/5` + `1/5` - `1/7` +...+ `1/97` - `1/99`
C= ( `1` - `1/99` ) + ( `1/3` - `1/3` ) + ( `1/5` - `1/5` ) +...+ ( `1/97` + `1/97` )
C= (`99/99` - `1/99` ) + `0` + `0` +...+ `0`
C= `98/99`
# `no` `name`
`học` `tốt`