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13 tháng 8 2016

\(A=4+4^2+4^3+...+4^{100}\)

\(A=\left(4+\text{ }4^2\right)+\left(4^3+4^4\right)+...+\left(4^{99}+4^{100}\right)\)

\(A=\left(1+4\right).\left(4\right)+\left(1+4\right).\left(4^3\right)+...+\left(1+4\right).\left(4^{99}\right)\)

\(A=5.\left(4+4^3+4^5+...+4^{99}\right)\)

Vậy A chia hết cho 5

Các bạn nha!

10 tháng 8 2019

\(B=4+4^2+.....+4^{100}\)

   \(=\left(4+4^2\right)+\left(4^3+4^4\right)+....+\left(4^{99}+4^{100}\right)\)

Vì các nhóm trên đều có chữ số tận cùng là 0 

\(\Rightarrow B⋮5\left(đpcm\right)\)

10 tháng 8 2019

\(B=4+4^2+4^3+...+4^{99}+4^{100}\)

\(4B=4^2+4^3+4^4+...+4^{100}+4^{101}\)

\(3B=4^{101}-4\)

\(B=\frac{4^{101}-4}{3}\)

27 tháng 12 2017

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28 tháng 12 2017

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\(A=\left(1+4+4^2+4^3+4^4\right)+...+4^{95}\left(1+4+4^2+4^3+4^4\right)\)

\(=341\cdot\left(1+...+4^{95}\right)⋮31\)

31 tháng 12 2015

Ta có:

A=(41+42)+(43+44)+...+(499+4100)

A=4.(1+4)+43.(1+4)+...+499.(1+4)

A=4.5+43.5+...+499.5

A=5.(4+43+...+499)

=>A chia hết cho 5

1 tháng 1 2016

bài này tớ đã biết nhưng chỉ thử các bạn thôi... cám ơn nhiều nha

 

22 tháng 10 2017

đặt A = 3 + 32 + 33 + 34 + ... + 399 + 3100

A = ( 3 + 32 ) + ( 33 + 34 ) + ... + ( 399 + 3100 )

A = 3 ( 1 + 3 ) + 33 ( 1 + 3 ) + ... + 399 ( 1 + 3 )

A = 3 . 4 + 33 . 4 + ... + 399 . 4

A = 4 . ( 3 + 33 + ... + 399 ) \(⋮\)4

12 tháng 4 2020

1. \(A=\frac{1}{2}-\frac{2}{5}+\frac{1}{3}+\frac{5}{7}-\frac{-1}{6}+\frac{-4}{35}+\frac{1}{41}\)

\(=\frac{1}{2}-\frac{2}{5}+\frac{1}{3}+\frac{5}{7}+\frac{1}{6}-\frac{4}{35}+\frac{1}{41}\)

\(=\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{6}\right)-\left(\frac{2}{5}-\frac{5}{7}+\frac{4}{35}\right)+\frac{1}{41}\)

\(=\left(\frac{5}{6}+\frac{1}{6}\right)-\left(\frac{-11}{35}+\frac{4}{35}\right)+\frac{1}{41}\)\(=1-\frac{-7}{35}+\frac{1}{41}=1+\frac{1}{5}+\frac{1}{41}=\frac{251}{205}\)

2. a) \(1+4+4^2+4^3+......+4^{99}=\left(1+4\right)+\left(4^2+4^3\right)+.......+\left(4^{98}+4^{99}\right)\)

\(=\left(1+4\right)+4^2\left(1+4\right)+.........+4^{98}\left(1+4\right)\)

\(=5+4^2.5+........+4^{98}.5=5\left(1+4^2+.....+4^{98}\right)⋮5\)( đpcm )

b) \(3^{n+2}-2^{n+2}+3^n-2^n=\left(3^{n+2}+3^n\right)-\left(2^{n+2}+2^n\right)\)

\(=3^n\left(3^2+1\right)-2^n\left(2^2+1\right)=3^n\left(9+1\right)-2^n\left(4+1\right)\)

\(=3^n.10-2^n.5=3^n.10-2^{n-1+1}.5=3^n.10-2^{n-1}.2.5\)

\(=3^n.10-2^{n-1}.10=10\left(3^n-2^{n-1}\right)⋮10\)( đpcm )

3 tháng 11 2023

A = 1/4 + 1/4² + 1/4³ + ... + 1/4⁹⁹

⇒ 4A = 1 + 1/4 + 1/4² + ... + 1/4⁹⁸

⇒ 3A = 4A - A

= (1 + 1/4 + 1/4² + ... + 1/4⁹⁸) - (1/4 + 1/4² + 1/4³ + ... + 1/4⁹⁹)

= 1 - 1/4⁹⁹

⇒ A = (1 - 1/4⁹⁹)/3

Do 1 - 1/4⁹⁹ < 1

⇒ (1 - 1/4⁹⁹)/3 < 1/3

Vậy A < 1/3

1 tháng 11 2015

\(A=1+4+4^2+...+4^{99}\)

\(A=\left(1+4+4^2+4^3\right)+\left(4^4+4^5+4^6+4^7\right)+...+\left(4^{96}+4^{97}+4^{98}+4^{99}\right)\)

\(A=85+4^7\left(1+4+4^2+4^3\right)...+4^{96}\left(1+4+4^2+4^3\right)\)

\(A=85+4^7.85+...+4^{96}.85\)

\(A=85.\left(1+4^7+...+4^{96}\right)\)

Vì 85 chia hết cho 17 nên A chia hết cho 17