Question

[Pé Mèo]

Tính :       \(\frac{1}{3\times5}+\frac{1}{5\times7}+\frac{1}{7\times9}...+\frac{1}{2009\times2011}\)

Answer 1

[Kudo Shinichi]

gọi biểu thức đó là A

\(A=\frac{1}{3.5}+\frac{1}{5.7}+.......+\frac{1}{2009.2011}\)

\(A=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+.......+\frac{1}{2009}-\frac{1}{2011}\right)\)

\(A=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{2011}\right)\)

\(A=\frac{1}{2}.\left(\frac{2008}{6033}\right)\)

\(A=\frac{1004}{6033}\)

mink nghĩ vậy bạn ạ

Answer 2

[Pé Mèo]

C.mơn bạn nha ! ^_^