Đặt: A = 1 + 1 + 1 + 1 +.....+ 1
$\overline{1 × 2}$ $\overline{2×3}$ $\overline{3 × 4}$ $\overline{4 × 5}$ $\overline{99 × 100}$
A = `1/1` - `1/2` + `1/2` - `1/3` + `1/3` - `1/4` +.......+ `1/99` - `1/100`
A = 1 - `1/100`
A = `99/100`
`=>` A = `99/100`