Question

1/1.3 1/3.5 1/5.7 ... 1/(2n-1)(2n 1) = n/2n 1?

Answer 1

let me fix it for you
should say:
1/(1*3) + 1/(3*5) + 1/(5*7) + ... + 1/(2n-1)(2n + 1) = n/(2n + 1)

Now what about it ???
Are you trying to prove it is true?
Try Induction.

Answer 2

1/(1*3) + 1/(3*5) + 1/(5*7) + ... + 1/(2n-1)(2n + 1) = n/(2n + 1)