Question

[Vũ Thị Thảo Phương]

1/1x3 + 1/3x5 + 1/5x7 + .....+ 1/ (2n+1)x(2n+3) =n+1/2n+3 

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Answer 1

[Trà My]

\(\frac{1}{1x3}+\frac{1}{3x5}+\frac{1}{5x7}+...+\frac{1}{\left(2n+1\right)x\left(2x+3\right)}=\frac{n+1}{2n+3}\)

=>\(2x\left(\frac{1}{1x3}+\frac{1}{3x5}+\frac{1}{5x7}+...+\frac{1}{\left(2n+1\right)x\left(2n+3\right)}\right)=2x\frac{n+1}{2n+3}\)

=>\(\frac{2}{1x3}+\frac{2}{3x5}+\frac{2}{5x7}+...+\frac{2}{\left(2n+1\right)\left(2n+3\right)}=\frac{2n+2}{2n+3}\)

=>\(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2n+1}-\frac{1}{2n+3}=\frac{2n+2}{2n+3}\)

=>\(1-\frac{1}{2n+3}=\frac{2n+2}{2n+3}\)

=>\(\frac{2n+2}{2n+3}=\frac{2n+2}{2n+3}\)

=>.....