I got this question in homework:
Find an expression for the sum
∑k=1+⋯+n.
and prove it using an induction.
I'm not even near finding the expression. What I did notice is that
if n is (for example) 5 then the sum would be
52−42+32−22+12
So the first number is always positive and from there on the sign changes.
Any tips on how do I contintue from this point on, assuming I'm in the right direction?
Thanks!
Answer
Hint.
1+2+3+4+⋯+n+n+n−1+n−2+n−3+⋯+1n+1+n+1+n+1+n+1+⋯+n+1
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