A=1/25.24+1/24.23+...+1/7.6+1/6.5

Đáp án:

$\frac{4}{25}$

Giải thích các bước giải:

$\frac{1}{25.24}+ \frac{1}{24.23}+...+\frac{1}{7.6}+ \frac{1}{6.5}$

$= \frac{1}{5.6}+ \frac{1}{6.7}+...+\frac{1}{23.24}+ \frac{1}{24.25}$

$= \frac{1}{5}- \frac{1}{6} + \frac{1}{6} - \frac{1}{7} +...+ \frac{1}{23} - \frac{1}{24} + \frac{1}{24} -\frac{1}{25}$

$=\frac{1}{5} - \frac{1}{25}$

$=\frac{4}{25}$