Tìm y ( 1/1x3 + 1/3x5 + 1/5x7 + 1/7x9 + 1/9x11 ) x y= 2/3 Mn giúp em với ạ, em cảm ơn nhiều!

$(\dfrac{1}{1\times3}+\dfrac{1}{3\times5}+\dfrac{1}{5\times7}+\dfrac{1}{7\times9}+\dfrac{1}{9\times11})\times y=\dfrac{2}{3}$

$2\times(\dfrac{1}{1\times3}+\dfrac{1}{3\times5}+\dfrac{1}{5\times7}+\dfrac{1}{7\times9}+\dfrac{1}{9\times11})\times y=\dfrac{2}{3}\times2$

 $\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+\dfrac{2}{9\times11})\times y=\dfrac{4}{3}$

$(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11})\times y=\dfrac{4}{3}$

$(1-\dfrac{1}{11})\times y=\dfrac{4}{3}$

$\dfrac{10}{11})\times y=\dfrac{4}{3}$

$y=\dfrac{4}{3}:\dfrac{10}{11}$

$y=\dfrac{22}{15}$

Vậy $y=\dfrac{22}{15}$