Toán Lớp 6: Chứng minh
A= 4 + 4^2 + 4^3 + …+ 4^120 ⋮ 5; 21; 17; 105
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Toán Lớp 6: Chứng minh
A= 4 + 4^2 + 4^3 + …+ 4^120 ⋮ 5; 21; 17; 105
Comments ( 2 )
A=(4+4^2)+(4^3+4^4)+……………+(4^119+4^120)
A=4.(1+4)+4^3.(1+4)+………….+4^119.(1+4)
A=4.5+4^3. 5+……………+4^119.5
A=5.(4+4^3+………………+4^119)
Vì 5vdots5
=>Avdots5
A=(4+4^2+4^3)+……..+(4^118+4^119+4^120)
A=4.(1+4+4^2)+………..+4^118.(1+4+4^2)
A=4.21+……………+4^118. 21
A=21.(4+…………..+4^118)
Vì 21vdots21
=>Avdots21
A=(4+4^2+4^3+4^4)+…………..+(4^117+4^118+4^119+4^120)
A=4.(1+4+4^2+4^3)+…………….+4^117.(1+4+4^2+4^3)
A=4.85+……………+4^117. 85
A=85.(4+……………+4^117)
Vì 85vdots17
=>Avdots17
A=(4+4^2+4^3+4^4+4^5+4^6)+…………..+(4^115+4^116+4^117+4^118+4^119+4^120)
A=4.(1+4+4^2+4^3+4^4+4^5)+…………….+4^115.(1+4+4^2+4^3+4^4+4^5)
A=1.1365+………………+4^115. 1365
A=1365.(1+………………+4^115)
Vì 1365vdots105
=>Avdots105