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cho so abc chia het cho 4 ( a;b;c la cac chu so chan khac 0) chung minh so bac chia het cho 4
Cho n so nguyen bat ki a;b;c;...;n
Chung Minh Rang : (a+b)+(b+c)+...+(z+n) la 1 so chan
chung minh rang neu 2 so a,b la 2 so nguyen khac 0 va a la boi cua b;b la boi cua a thi:a=b hoac a=-b
giup mk nhe mk can gap
chung minh rang voi a,b(a>b) la cac chu so khac 0 thi (abab-baba) chia het cho 9 va 101
Chung minh rang: moi n thuoc z ( n khac 0,n khac -1) thi : Q =1\1.2+1\2.3+1\3.4+......+1\n(n+1) khong phai la so nguyen
cho A la tap hop cac so tu nhien nho hon 10,
B la tap hop cac so chan,
N* la tap hop cac so tu nhien khac 0.
dung ki hieu tap hop con de the hien quan he cua moi tren voi tap hop N cac so tu nhien
Tim 3 so tu nhien a,b,c nho nhat khac 0 sao cho 64a=80b=96c
Chung to rang (7n+10)va (5n+7) la 2 so nguen to cung nhau (n thuoc N)
CMR: Tong cua n so TN chan dau tien khac 0 ko the la 1 so chinh phuong.
chung minh voi n la so tu nhien thi (n+3).(n+4) la 1 so chan
