Ta có:\(\frac{1}{5}>\frac{1}{6}>...>\frac{1}{19}\)
=>B=\(\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+...+\frac{1}{19}>\frac{1}{4}+\frac{1}{19}+\frac{1}{19}+...+\frac{1}{19}\)(15 lần 1/19)
=>B>1/4+15/19=79/76>1
=>B>1
Cho B=\(\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+...+\frac{1}{19}\)Hay chung to rang B>1
cho \(B=\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+...+\frac{1}{19}\)
chung to rang B >1
cho B = .\(\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+.....+\frac{1}{19}\) Hay chung to B< 1
cho B=1/4+1/5+1/6+...+1/19. Chung to rang B>1
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chung minh rang B= 1/5+1/6+1/7+.....+1/19<11/6
Cho B=1/5+1/6+1/7+...+1/17 .Chung to rang B<2
B=1/4+1/5+1/6+.....+1/19.Chung to B>1
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
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