Thực hiện phép tính sau : A = ` 1/30 + 1/42 + 1/56 + 1/72 + … + 1/380 ` 31/08/2021 Bởi Amaya Thực hiện phép tính sau : A = ` 1/30 + 1/42 + 1/56 + 1/72 + … + 1/380 `
$A=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+…+\frac{1}{380}$ $=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+…+\frac{1}{19.20}$ $=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+…+\frac{1}{19}-\frac{1}{20}$ $=\frac{1}{5}-\frac{1}{20}$ $=\frac{3}{20}.$ Bình luận
Đáp án: `3/20` Giải thích các bước giải: `1/30+1/42+1/56+1/72+…+1/380` `=1/5.6+1/6.7+1/7.8+1/8.9+…+1/19.20` `=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+…+1/19-1/20` `=1/5-(1/6-1/6+1/7-1/7+1/8-1/8+1/9-…-1/19+1/20)` `=1/5-1/20` `=3/20` Bình luận
$A=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+…+\frac{1}{380}$
$=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+…+\frac{1}{19.20}$
$=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+…+\frac{1}{19}-\frac{1}{20}$ $=\frac{1}{5}-\frac{1}{20}$
$=\frac{3}{20}.$
Đáp án:
`3/20`
Giải thích các bước giải:
`1/30+1/42+1/56+1/72+…+1/380`
`=1/5.6+1/6.7+1/7.8+1/8.9+…+1/19.20`
`=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+…+1/19-1/20`
`=1/5-(1/6-1/6+1/7-1/7+1/8-1/8+1/9-…-1/19+1/20)`
`=1/5-1/20`
`=3/20`