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29 tháng 11 2016

ta có:=(a+a^2)+(a^3+a^4)+...+(a^29+a^30)

=a(1+a)+a^3(1+a)+...+a^29(1+a) chia hết cho (a+1) (điều phải chứng minh)

27 tháng 12 2017

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28 tháng 12 2017

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27 tháng 12 2017

Có : a+a^2+a^3+a^4+....+a^29+a^30

= (a+a^2)+(a^3+a^4)+....+(a^29+a^30)

= a.(a+1)+a^3.(a+1)+....+a^29.(a+1)

= (a+1).(a+a^3+...+a^29) chia hết cho a+1

=> ĐPCM

k mk nha

27 tháng 12 2017

\(a+a^2+a^3+a^4+...+a^{29}+a^{30}\)

\(=\left(a+a^2\right)+\left(a^3+a^4\right)+...+\left(a^{29}+a^{30}\right)\)

\(=a\left(a+1\right)+a^3\left(a+1\right)+...+a^{29}\left(a+1\right)\)

\(=\left(a+1\right)\left(a+a^3+...+a^{29}\right)\)

Mà a là STN \(\Rightarrow\left(a+1\right)\left(a+a^3+...+a^{29}\right)⋮\left(a+1\right)\)

\(\Rightarrow a+a^2+a^3+a^4+...+a^{29}+a^{30}⋮\left(a+1\right)\)

Ta có 

(a+a^2+a^3+........a^29+a^30)

=(a+a^2)+(a^3+a^4)+........(a^29+a^30)

=a(1+a)+a^3(1+a)+.........a^29(1+a)

=a+1(a+a^3+.......+a^29)chia hết cho a+1

nhớ k cho mình nha

7 tháng 7 2015

a)A=1+4+4^2+4^3+...+4^11

=(1+4+42)+(43+44+45)+(46+47+48)+(49+410+411)

=(1+4+42)+(43.1+43.4+43.42)+(46.1+46.4+46.42)+(49.1+49.4+49.42)

=(1+4+42).1+43.(1+4+42)+46.(1+4+42)+49.(1+4+42)

=21.1+43.21+46.21+49.21

=21.(1+43+46+49)

=> A chia het cho 21

b)A=1+4+4^2+4^3+...+4^11

=(1+4+42+43+44+45)+(46+47+48+49+410+411)

=(1+4+42+43+44+45)+(46.1+46.4+46.42+46.43+46.44+46.45)

=(1+4+42+43+44+45).1+46.(1+4+42+43+44+45)

=1365.1+46.1365

=1365.1+46.1365

=1365.(1+46)

vì nên 1365 chia hết cho 105 nên A chia het cho 105

14 tháng 10 2017

Còn phần c nưa bạn trieu dang ơi