Thực hiện phép tính sau : M = `2/(2.3.4) + 2/(3.4.5) + …….. + 2/(19.20.21)` 05/09/2021 Bởi Melody Thực hiện phép tính sau : M = `2/(2.3.4) + 2/(3.4.5) + …….. + 2/(19.20.21)`
$M$ = $\dfrac{2}{2.3.4}$ +$\dfrac{2}{3.4.5}$ +…+$\dfrac{2}{19.20.21}$ $M$ = $\dfrac{1}{2.3}$ – $\dfrac{1}{3.4}$ + $\dfrac{1}{3.4}$ – $\dfrac{1}{4.5}$ +…+ $\dfrac{1}{19.20}$- $\dfrac{1}{20.21}$ $M$ = $\dfrac{1}{2.3}$-$\dfrac{1}{20.21}$ $M$ = $\dfrac{1}{6}$-$\dfrac{1}{420}$ $M$ = $\dfrac{70}{420}$ – $\dfrac{1}{420}$ $M$ = $\dfrac{69}{420}$ = $\dfrac{23}{140}$ $Vậy$ $M$ = $\dfrac{23}{140}$ $chúc$ $bạn$ $học$ $tốt$ $nhé$ Bình luận
Giải thích các bước giải: M=1/2.3-1/3.4+1/3.4-1/4.5+…+1/19.20-1/20.21 M=1/2.3-1/20.21 M=9/20 Bình luận
$M$ = $\dfrac{2}{2.3.4}$ +$\dfrac{2}{3.4.5}$ +…+$\dfrac{2}{19.20.21}$
$M$ = $\dfrac{1}{2.3}$ – $\dfrac{1}{3.4}$ + $\dfrac{1}{3.4}$ – $\dfrac{1}{4.5}$ +…+ $\dfrac{1}{19.20}$- $\dfrac{1}{20.21}$
$M$ = $\dfrac{1}{2.3}$-$\dfrac{1}{20.21}$
$M$ = $\dfrac{1}{6}$-$\dfrac{1}{420}$
$M$ = $\dfrac{70}{420}$ – $\dfrac{1}{420}$
$M$ = $\dfrac{69}{420}$ = $\dfrac{23}{140}$
$Vậy$ $M$ = $\dfrac{23}{140}$
$chúc$ $bạn$ $học$ $tốt$ $nhé$
Giải thích các bước giải:
M=1/2.3-1/3.4+1/3.4-1/4.5+…+1/19.20-1/20.21
M=1/2.3-1/20.21
M=9/20