=>B=\(\dfrac{1}{4.4}+\dfrac{1}{6.6}+\dfrac{1}{8.8}+...+\dfrac{1}{2006.2006}\)

=>B<\(\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+...+\dfrac{1}{2005.2007}\)

=>B<\(\dfrac{2}{2}.\left(\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+...+\dfrac{1}{2005.2007}\right)\)

=>B<\(\dfrac{1}{2}.\left(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+...+\dfrac{2}{2005.2007}\right)\)

=>B<\(\dfrac{1}{2}.\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{2005}-\dfrac{1}{2007}\right)\)

=>B<\(\dfrac{1}{2}.\left(\dfrac{1}{3}+\dfrac{1}{5}-\dfrac{1}{5}+...+\dfrac{1}{2005}-\dfrac{1}{2005}-\dfrac{1}{200}\right)\)(xin lỗi, đoạn cuối (chỗ 200 í )là 2007 nhá

=>B<\(\dfrac{1}{2}.\left(\dfrac{1}{3}-\dfrac{1}{2007}\right)\)

=>B<\(\dfrac{1}{2}.\dfrac{668}{2007}\)

=>B<\(\dfrac{1.668}{2.2007}\)

=>B<\(\dfrac{1.668:2}{2.2007:2}\)

=>B<\(\dfrac{334}{2007}\)

Tick cho tôi nha :D

Ta thấy : \(\frac{1}{4^2}< \frac{1}{4.5};\frac{1}{6^2}< \frac{1}{5.6};...;\frac{1}{2006^2}< \frac{1}{2005.2006}\)

\(\Rightarrow B=\frac{1}{4^2}+\frac{1}{6^2}+...+\frac{1}{2006^2}< \frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{2005.2006}\)

\(\Leftrightarrow B< \frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{2005}-\frac{1}{2006}\)

\(\Leftrightarrow B< \frac{1}{4}-\frac{1}{2006}=\frac{1001}{4012}\)

Mà \(\frac{1001}{4012}< \frac{334}{2007}\Rightarrow B< \frac{334}{2007}\)

\(B< \frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{2006.2008}\)

\(2B< \frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{2006.2008}=\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{2006}-\frac{1}{2008}=\frac{1}{4}-\frac{1}{2008}=\frac{501}{2008}\)\(B< \frac{501}{4016}< \frac{501}{4014}< \frac{668}{4014}=\frac{334}{2007}\)

Vậy:.....

1/6^2 < 1/5.6?????????

mik sẽ trả lời pạn sau nhé ..sorry mik pạn ti......

Mai ơi! bạn khùng hả? ko trả lời thì thôi lại còn vào chỗ trả lời để sorry