Cho B=1/5+1/6+1/7+...+1/17 .Chung to rang B<2
Chung minh rang 1/15+1/16+1/17+1/18+.....+1/44 > 5/6
Chung minh rang
1 be hon 1/5+1/6+.....+1/16+1/17 be hon 2
chung to rang B= 1/2^2+1/3^2+1/4^2+1/5^2+1/6^2+1/7^2+1/8^2<1
chung to rang tong B sau lon hon 1/2 B=1/12+1/13+1/14+1/15+1/16+1/17+1/18+1/19+1/20+1/21+1/22
chung to rang B=1/2^2+1/3^2+1/4^2+1/5^2+1/6^2+1/7^2+1/8^2<1
ai lam duoc minh tick cho
BAI 1: chung to rang 175 + 244 + -1321 chia het cho 10
BAI 2:chung minh rang voi moi so tu nhien n :
a) 74n -1 chia het cho 5
b) 34n+1 +2 chia het cho 5
chung minh rang tong sau khong phai la so tu nhien
1/2+1/3+1/4+1/5+1/6+...+1/16
Cho S=1/2+1/6+1/7+1/8+...............1/16+1/17.Hãy chung tỏ S<2
