$\frac{4}{3×7}$ + $\frac{5}{7×12}$ +$\frac{1}{12×13}$ + $\frac{7}{13×20}$ + $\frac{3}{20×23}$
$\frac{4}{3×7}$ + $\frac{5}{7×12}$ +$\frac{1}{12×13}$ + $\frac{7}{13×20}$ + $\frac{3}{20×23}$
By Kinsley
By Kinsley
$\frac{4}{3×7}$ + $\frac{5}{7×12}$ +$\frac{1}{12×13}$ + $\frac{7}{13×20}$ + $\frac{3}{20×23}$
Đáp án:
Giải thích các bước giải:
`\frac{4}{3×7} + \frac{5}{7×12} + \frac{1}{12×13} + \frac{7}{13×20} + \frac{3}{20×23}`
= `\frac{1}{3} – \frac{1}{7} + \frac{1}{7} – \frac{1}{12} + …. + \frac{1}{20} – \frac{1}{23}`
= `\frac{1}{3} – \frac{1}{23}`
= `\frac{23}{69} – \frac{3}{69}`
= `\frac{20}{69}`
`=1/3-1/7+1/7-1/12+1/12-1/13+1/13-1/20+1/20-1/23`
`=1/3-1/23`
`=20/69`