=>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