`1/3`+`1/6`+`1/12`+`1/20`+`1/30`+`1/42`+`1/56`+`1/72` 03/09/2021 Bởi Sadie `1/3`+`1/6`+`1/12`+`1/20`+`1/30`+`1/42`+`1/56`+`1/72`
Đáp án: `13/18` Giải thích các bước giải: `1/3 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72` `= 1/3 + 1/(2 X 3) + 1/(3 X 4) + 1/(4 X 5) + 1/(5 X 6) + 1/(6 X 7) + 1/(7 X 8) + 1/(8 X 9)` `= 1/3 + 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + 1/5 – 1/6 + 1/6 – 1/7 + 1/7 – 1/8 + 1/8 – 1/9` `= 1/3 + 1/2 – 1/9` `= 6/18 + 9/18 – 2/18` `= 15/18 – 2/18` `= 13/18` Bình luận
$\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}\\=\dfrac{1}{3}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}\\=\dfrac{1}{3}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}\\=\dfrac{1}{3}+\dfrac{1}{2}-\dfrac{1}{9}=\dfrac{13}{18}$ Bình luận
Đáp án: `13/18`
Giải thích các bước giải:
`1/3 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72`
`= 1/3 + 1/(2 X 3) + 1/(3 X 4) + 1/(4 X 5) + 1/(5 X 6) + 1/(6 X 7) + 1/(7 X 8) + 1/(8 X 9)`
`= 1/3 + 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + 1/5 – 1/6 + 1/6 – 1/7 + 1/7 – 1/8 + 1/8 – 1/9`
`= 1/3 + 1/2 – 1/9`
`= 6/18 + 9/18 – 2/18`
`= 15/18 – 2/18`
`= 13/18`
$\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}\\=\dfrac{1}{3}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}\\=\dfrac{1}{3}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}\\=\dfrac{1}{3}+\dfrac{1}{2}-\dfrac{1}{9}=\dfrac{13}{18}$