bài 1:tinh nhanh A: 6/1*4+6/4*7+6/7*10+6/10*13+…..+6/2017*2020 các bạn ơi dấu * là dấu nhân nha 20/08/2021 Bởi Peyton bài 1:tinh nhanh A: 6/1*4+6/4*7+6/7*10+6/10*13+…..+6/2017*2020 các bạn ơi dấu * là dấu nhân nha
$\dfrac{6}{1.4}$ $+$ $\dfrac{6}{4.7}$ $+$ $…..$ $+$ $\dfrac{6}{2017.2020}$ $=$ $2$$.$ $($ $\dfrac{3}{1.4}$ $+$ $\dfrac{3}{4.7}$ $+$ $…..$ $+$ $\dfrac{3}{2017.2020}$ $)$ $=$ $2$ $.$ $($ $1$ $-$ $\dfrac{1}{4}$ $+$ $\dfrac{1}{4}$ $-$ $\dfrac{1}{7}$ $+$ $…..$ $+$ $\dfrac{1}{2017}$ $-$ $\dfrac{1}{2020}$ $)$ $=$ $2$ $.$ $($ $1$ $-$ $\dfrac{1}{2020}$ $)$ $=$ $2$ $.$ $\dfrac{2019}{2020}$ $=$ $\dfrac{4038}{2020}$ $=$ $\dfrac{2019}{1010}$ Vậy $A$ $=$ $\dfrac{2019}{1010}$ Học tốt nha! Bình luận
$\dfrac{6}{1.4}$ $+$ $\dfrac{6}{4.7}$ $+$ $…..$ $+$ $\dfrac{6}{2017.2020}$
$=$ $2$$.$ $($ $\dfrac{3}{1.4}$ $+$ $\dfrac{3}{4.7}$ $+$ $…..$ $+$ $\dfrac{3}{2017.2020}$ $)$
$=$ $2$ $.$ $($ $1$ $-$ $\dfrac{1}{4}$ $+$ $\dfrac{1}{4}$ $-$ $\dfrac{1}{7}$ $+$ $…..$ $+$ $\dfrac{1}{2017}$ $-$ $\dfrac{1}{2020}$ $)$
$=$ $2$ $.$ $($ $1$ $-$ $\dfrac{1}{2020}$ $)$
$=$ $2$ $.$ $\dfrac{2019}{2020}$
$=$ $\dfrac{4038}{2020}$
$=$ $\dfrac{2019}{1010}$
Vậy $A$ $=$ $\dfrac{2019}{1010}$
Học tốt nha!
Giải thích các bước giải:
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