Question 1081833

Hey! 

I'm trying to figure out what the general formula is based on the following sequence: {2/3, -3/5, 4/7, -5/9}

So I believe that the numerator is something like (n+1) but I can't for the life of me figure out the bottom or the negatives.. 

Thanks!
<pre><b>The correct rule is: {{{highlight_green(((n + 1)/(2n + 1)) * - 1^(n + 1)))}}}</b>