Question

Cho minh hoi bai nay vs:

Chung to S=\(\dfrac{1}{4}\)+\(\dfrac{2}{4}\)+...+\(\dfrac{10}{4}\)<14

Chung to S=\(\dfrac{1}{6}+\dfrac{1}{7}+...+\dfrac{1}{19}< 2\)

Chung to S=\(\dfrac{1}{10}+\dfrac{1}{4}+...+\dfrac{1}{100}>1\)

Answer 1

— S = 1/4 + 2/4 +...+10/4 (1)

= 1 + 1/4 + 2/4 +...+ 9/4 (2)

=> Lấy (2) trừ đi (1) ta được:

1 — 10/4 = —6/4

Vì 14 = 14/1 = 84/6 mà —6/4 < 84/6

Do đó S < 14