Question

Tính:

1/5 x 7 + 1/ 7 x 9 +....+ 1/2011 x 2013
Ét u ét à nhầm Ét ô ét 

Answer 1

toán 5 mà khó thế bn

Answer 2

\(A=\dfrac{1}{2}\times\left(\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{2011}-\dfrac{1}{2013}\right)=\dfrac{1}{2}\times\left(\dfrac{1}{5}-\dfrac{1}{2013}\right)=\dfrac{1004}{10065}\)