Question

B=1/12+1/13+1/14+1/15+1/16+1/17+1/18+1/19+1/20+1/21+1/22

Chứng tỏ B>1/2

Answer 1

\(B=\frac{1}{12}+\frac{1}{13}+...+\frac{1}{22}\)có 11 số hạng

Ta có: \(\frac{1}{12}>\frac{1}{22}\)

           \(\frac{1}{13}>\frac{1}{22}\)

              .............

           \(\frac{1}{22}=\frac{1}{22}\)

\(\Rightarrow B>\left(\frac{1}{22}+\frac{1}{22}+...+\frac{1}{22}\right)=\frac{11}{22}=\frac{1}{2}\)