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## Homework Statement

for any positive interget n determine

a) SUM(from i=0 to n) of

__(-1)^i__

i!(n-i)!

b) SUM (from i=0 to n) of

__1__

i!(n-1)!

## Homework Equations

## The Attempt at a Solution

a) well i didnt realyl know how to start. i found that with

n=1 then it becomes 1+1

n=2 .5+1+.5

n=3 1/3! + .5 +.5 +1/3!

n=4 1/4! +1/3! +.25 +1/3! +1/4!

n=4 1/5! +1/4! +.083333 +.083333 +1/4! +1/5!

so i guess what i need is how do i get the middle term?

or am i going about it wrong?

for b) i know the sum is always 0, because ichecked it on my calculator. but i don't know hwo to prive that