Question

B  = 1/4 + 1/5 + 1/6 + ...+ 1/19 chứng minh B>1

Answer 1

Nhok tham khao bai ben duoi i

Answer 2

Ta có B = 1/4 + 1/5 + 1/6+1/7+..+1/19

           >1/19+1/19+..+1/19

           =19/19=1

  Vậy B>1

Answer 3

\(B=\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+...+\frac{1}{19}\)

\(\Rightarrow B>\frac{1}{4}+\frac{1}{20}+\frac{1}{20}+...+\frac{1}{20}\)(15 số hạng \(\frac{1}{20}\))

\(\Rightarrow B>\frac{1}{4}+\frac{1}{20}.15\)

\(\Rightarrow B>\frac{1}{4}+\frac{15}{20}=1\)

Vậy B > 1 (đpcm)