Toán Lớp 6: 1+2+2^2+2^3+2^4+….+2^89 mà chia hết cho 85
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Toán Lớp 6: 1+2+2^2+2^3+2^4+….+2^89 mà chia hết cho 85
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A=1+2+2^2+2^3+2^4+………………….+2^89
A=(1+2+2^2+2^3+2^4+2^5+2^6+2^7)+………………….+(2^82+2^83+2^84+2^85+2^86+2^87+2^88+2^89)
A=1.(1+2+2^2+2^3+2^4+2^5+2^6+2^7)+…………………….+2^82.(1+2+2^2+2^3+2^4+2^5+2^6+2^7)
A=1.225+…………………+2^82. 225
A=225.(1+………………………..+2^82)
Vì 225vdots85
=>Avdots85
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