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TD
2
28 tháng 3 2017
\(\dfrac{5}{7}x-x=1\dfrac{1}{7}\\ < =>\dfrac{5}{7}x-x=\dfrac{8}{7}\\ < =>\left(\dfrac{5}{7}-\dfrac{7}{7}\right)x=\dfrac{8}{7}\\ < =>-\dfrac{2}{7}x=\dfrac{8}{7}\\ =>x=\dfrac{\dfrac{8}{7}}{-\dfrac{2}{7}}=-4\)
9 tháng 10 2021
chia hết.chấm hếtttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt
CD
22
NK
7
H
1
NY
25 tháng 12 2019
https://vndoc.com/de-kiem-tra-hoc-ki-i-lop-6-mon-toan-de-so-1-1/download
#Châu's ngốc
X
24 tháng 3 2019
Ta có : \(A=3+3^2+3^3+3^4+...+3^{25}\)
\(=3+\left(3^2+3^3+3^4\right)+...+\left(3^{23}+3^{24}+3^{25}\right)\)
\(=3+3\left(3+3^2+3^3\right)+...+3^{22}\left(3+3^2+3^3\right)\)
\(=3+3.39+...+3^{22}.39\)
\(=3+39\left(3+...+3^{22}\right)\)
\(\Rightarrow A\)chia cho 39 dư 3
\(\Rightarrow A\)không chia hết cho 39 ( đpcm )