- #1
roadrunner
- 103
- 0
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