Question

Giúp mình với mình cần gấp

Answer 1

`2/(3.5) + 2/(5.7) + 2/(7.9) + .... + 2/(37.39)`

`=2 . (1/(3.5) + 1/(5.7) + .... + 1/(37.39)`

`=2 .[ 1/2 .(1/3 -1/5 + 1/5 -1/7 +....+1/37 -1/39)]`

`= 1/3 - 1/39`

`=4/13`

Answer 2

\(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+..+\dfrac{2}{37.39}\)

=\(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+..+\dfrac{1}{37}-\dfrac{1}{39}\)

=\(\dfrac{1}{3}-\dfrac{1}{39}\)

=\(\dfrac{4}{13}\)

Answer 3

\(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+...+\dfrac{2}{37.39}\\ =\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+...+\dfrac{1}{37.39}\\ =\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{37}-\dfrac{1}{39}\\ =\dfrac{1}{3}-\dfrac{1}{39}\\ =\dfrac{13}{39}-\dfrac{1}{39}\\ =\dfrac{4}{13}\)

Answer 4

\(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+...+\dfrac{2}{37.39}\) 

\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{37}-\dfrac{1}{39}\) 

\(=\dfrac{1}{3}-\dfrac{1}{39}\) 

\(=\dfrac{4}{13}\)