It might help to know why the above works.. basically you are factoring out a k! out of both terms.
[MATH]k! + (k+1)! = k! + (k+1)*k!= k!* (1+k+1)[/MATH]
You can apply that idea to the entire bottom of the fraction. Then you'll be able to simply stuff after that. The following limit may be helpful . It's likely you do not need to prove this fact because the proof is a bit difficult.
[MATH] \sum_{n=1}^{\infty} \frac{1}{n!} = e [/MATH]
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