S = (1+5)+(5^2+5^3)+(5^4+5^5)+(5^6+5^7)
= 6+5^2.(1+5)+5^4.(1+5)+5^6.(1+5)
= 6+5^2.6+5^4.6+5^6.6
= 6.(1+5^2+5^4+5^6) chia hết cho 6
=> ĐPCM
k mk nha
(1+5)+(5^2+5^3)+........+(5^6+5^7)
=6+5^2(1+5)+......+5^6(1+5)
=6+5^2 . 6 +.....+5^6 . 6
= 6 ( 5^2+.....+5^6)
Suy ra S chia hết cho 6
\(S=\left(1+5\right)+\left(5^2+5^3\right)+\left(5^4+5^5\right)+\left(5^6+5^7\right)\)
\(=6+5^2\times6+5^4\times6+5^6\times6\)
\(=6\left(1+5^2+5^4+5^6\right)\)chia hết cho 6
=> S chia hết cho 6 =>ĐPCM
S=1+5+52+53+54+55+56+57=(1+5)+(52+53)+(54+55)+(56+57)=(1+5)+52(1+5)+54(1+5)+56(1+5)=6+52*6+546+56*6=6(1+52+54+56) chia hết cho 6 (đpcm)
Vậy S chia hết cho 6
ta thay 1+ 5 =6 chia het cho 6
52+5 mu 3 =5.(5+1)=5.6 chia het cho 6
...............
5 mu 6+5 mu 7=5 mu 5.(5+1) chia het cho 6 (dpcm)
S=6+(5^2+5^3)+(5^4+5^5)+(5^6+5^7)
S=6+25.(1+5)+5^4.(1+5)+5^6.(1+5)
S=6.(1+25+5^4+5^6)chia hết cho 6
5S\(=5+5^2+5^3+...+5^7+5^8\)
\(5S-S=4S=5^8-1\)
\(4S=390624\)
\(S=97656\) Mà 97656 \(⋮\)3
\(\Rightarrow S⋮3\)
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