Tìm chữ số a , biết 5a793a4 chia hết cho 9
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A=5.415.99-4.320.89
A=5.(22)5.(32)9-22.320.(23)9
A=5.230.318-22.320.227
A=5.230.318-229.320
A=229.318.(5.2-32)
A=229.318
B=5.29.619-7.229.276
B=5.29.(2.3)9-7.229.(33)6
B=5.22.219.319-7.229.318
B=5.228.319-7.229.318
B=228.318.(5.3-7.2)
B=228.318
=>A:B= \(\frac{2^{29}.3^{18}}{2^{28}.3^{18}}\)
A:B=2
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La 5 vi o bai xet chu so tan cung cua phep tinh co noi tong 5 so tu nhien lien tiep la 5 hoac 0
VD : 1+2+3+4+5= 15
co phep tinh ma tong cua 5 so hang co tan cung la 0 nhu :
0+1+2+3+4= 10
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6x+1-6x=180
6x.6-6x=180
6x(6-1)=180
6x.5=180
6x=180:5
6x=36=62
suy ra x=2
6x+1 - 6x = 180
<=> 6x ( 6 - 1 ) = 180
<=> 6x . 5 = 180
<=> 6x = 36
<=> 6x = 62
=> x = 2
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Ta có: 8^8+2^20=(2^3)^8+2^20
=2^24+2^20
=2^20(2^4+1)
=2^20 * 17 chia hết cho 17
Vậy 8^8+2^20 chia hết cho 17 (Điều phải chứng minh)
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