- #1
Seydlitz
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Homework Statement
Prove that ##\binom{-1}{k}=(-1)^k##
The Attempt at a Solution
Using induction on ##k##,
##\binom{-1}{0}=1## which is true also for ##(-1)^0=1##
Assuming ##\binom{-1}{k}=(-1)^k##, then ##\binom{-1}{k+1}=(-1)^{k+1}##
Indeed when ##n=-1##, we can write rewrite this ##\frac{n!}{k!(n-k)!}## as ##\frac{(-1)^k(k)!}{k!}## to avoid negative factorial. Hence ##\binom{-1}{k+1}=\frac{(-1)^k(k+1)!}{(k+1)!}=(-1)^{k+1}##.
##\blacksquare##
I just want to confirm if my proof by induction method is valid.
Thank You