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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(3+3^2+.....+3^{99}\)
\(=\left(3+3^2+3^3\right)+\left(3^4+3^5+3^6\right)+...+\left(3^{97}+3^{98}+3^{99}\right)\)
\(=39+3^3\left(3+3^2+3^3\right)+........+3^{96}\left(3+3^2+3^3\right)\)
\(=39+3^3\cdot39+...+3^{96}\cdot39\)
\(=39\left(1+3^3+....+3^{96}\right)\)
Vì \(39⋮13\Rightarrow39\in B\left(13\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
b)
=>2x+1=3/5
2x=3/5-1
2x=-2/5
x=-2/5:2
x=-1/5
hoặc:
2x+1=-3/5
2x=-3/5-1
2x=-8/5
x=-8/5:2
x=-4/5
=>x=-1/5 hoặc x=-4/5
\(a.x^{2017}=x\)
Vì 0^2017 = 0
1^2017 = 1
=> x = 0 hoặc x = 1
![](https://rs.olm.vn/images/avt/0.png?1311)
3\(^{2x}\) = 81
=> 3\(^{2x}\) = 3\(^4\)
=> 2x = 4
=> x = 2
Vậy....
Ta có: 3^2x-1=80
<=> 3^2x=81
<=> 3^2x=3^4
<=> 2x=4
<=> x=2
Vậy x=2
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\overline{ab}+\overline{ba}\)
\(=10a+b+10b+a\)
\(=11a+11b\)
\(=11.\left(a+b\right)⋮11\)
Vậy \(\left(\overline{ab}+\overline{ba}\right)⋮11\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{x+4}{3}=\dfrac{x-11}{-6}\)
\(\dfrac{2x+8}{6}=\dfrac{-x+11}{6}\)
\(\Leftrightarrow2x+8=-x+11\)
\(\Leftrightarrow3x=3\)
\(\Leftrightarrow x=1\)
=7x32+2017-a -2x32017-a
=32017-ax(7x9-2)
=32017-ax61 là snt khi và chỉ khi 32017-a=1 hay a=2017
chúc bạn học tốt
HYC-23/1/2022