Find a formula that generates a sequence

[nicnicman]

Homework Statement

Find a formula that generates the sequence:

2/(3 x 4), -3/(4 x 5), 4/(5 x 6), -5/(6 x 7), . . .

Homework Equations

The Attempt at a Solution

Here is what I have so far:

a_n = -1(n/((n + 1)(n + 2)))

Now, I'm stuck. The formula generates a negative number every time. I need a negative number every other time.
Any suggestions?

 

[Dick]

Use something like (-1)^n?

 

[nicnicman]

Yeah, that will work. Thanks!