Đáp án:
A = $\frac{-97}{99}$
Giải thích các bước giải:
A = $\frac{1}{99}$ - $\frac{1}{99.98}$ - $\frac{1}{98.97}$ -.....- $\frac{1}{3.2}$ - $\frac{1}{2.1}$
A = $\frac{1}{99}$ - ( $\frac{1}{2.1}$ + $\frac{1}{3.2}$ + ...... $\frac{1}{98.97}$ + $\frac{1}{99.98}$ )
A = $\frac{1}{99}$ - ( 1 - $\frac{1}{2}$ + $\frac{1}{2}$ - $\frac{1}{3}$ +........+ $\frac{1}{97}$ - $\frac{1}{98}$ + $\frac{1}{98}$ - $\frac{1}{99}$ )
A = $\frac{1}{99}$ - ( 1 - $\frac{1}{99}$ )
A = $\frac{1}{99}$ - $\frac{98}{99}$
A = $\frac{-97}{99}$
