Đáp án:
$\frac{8}{9}$- $\frac{1}{72}$- $\frac{1}{56}$ -$\frac{1}{42}$ -...-$\frac{1}{6}$ -$\frac{1}{2}$
=$\frac{8}{9}$- ($\frac{1}{72}$+ $\frac{1}{56}$ +$\frac{1}{42}$ +...+$\frac{1}{6}$ +$\frac{1}{2}$ )
=$\frac{8}{9}$- ($\frac{1}{8.9}$+$\frac{1}{8.7}$ +$\frac{1}{7.6}$ +...+$\frac{1}{3.2}$ +$\frac{1}{2.1}$ )
=$\frac{8}{9}$-( $\frac{1}{9}$ -$\frac{1}{8}$ +$\frac{1}{8}$ -$\frac{1}{7}$+...+ $\frac{1}{2}$- 1)
=$\frac{8}{9}$-( 1- $\frac{1}{9}$ )
=0
