Toán A=5/20+5/30+5/42+…+5/420 ai nhanh nhất tick nha 17/11/2021 By Ariana A=5/20+5/30+5/42+…+5/420 ai nhanh nhất tick nha
Đáp án: Giải thích các bước giải: $A=\dfrac{5}{20}+\dfrac{5}{30}+\dfrac{5}{42}+…+\dfrac{5}{420}$ $ $ $=5.(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+…+\dfrac{1}{20.21})$ $ $ $=5.(\dfrac{1}{4}-\dfrac{1}{21})$ $ $ $=5.(\dfrac{21}{84}-\dfrac{4}{84})$ $ $ $=5.\dfrac{17}{84}$ $ $ $=\dfrac{85}{84}$ Trả lời
`A=5/20 + 5/30 + 5/42 +…+ 5/420` `= 5/4.5 + 5/5.6 + 5/6.7 +…+ 5/20.21` `= 5.(1/4.5 + 1/5.6 + 1/6.7 +…+ 1/20.21)` `= 5.(1/4 – 1/5 + 1/5 – 1/6 + 1/6 -1/7 +…+ 1/20 – 1/21)` `= 5.(1/4 – 1/21)` `= 5 . 17/84 = 85/84` Trả lời
Đáp án:
Giải thích các bước giải:
$A=\dfrac{5}{20}+\dfrac{5}{30}+\dfrac{5}{42}+…+\dfrac{5}{420}$
$ $
$=5.(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+…+\dfrac{1}{20.21})$
$ $
$=5.(\dfrac{1}{4}-\dfrac{1}{21})$
$ $
$=5.(\dfrac{21}{84}-\dfrac{4}{84})$
$ $
$=5.\dfrac{17}{84}$
$ $
$=\dfrac{85}{84}$
`A=5/20 + 5/30 + 5/42 +…+ 5/420`
`= 5/4.5 + 5/5.6 + 5/6.7 +…+ 5/20.21`
`= 5.(1/4.5 + 1/5.6 + 1/6.7 +…+ 1/20.21)`
`= 5.(1/4 – 1/5 + 1/5 – 1/6 + 1/6 -1/7 +…+ 1/20 – 1/21)`
`= 5.(1/4 – 1/21)`
`= 5 . 17/84 = 85/84`