Wednesday, 17 February 2016

real analysis - If a polynomial p(x) is divisible by (x-a)^n where nϵℕ and n≥2, then p(x) is divisible by (x-a)^(n-1)



I have no idea how to begin, I do know that if p(x) is divisible by (xa)n then we should have p(x)=(xa)nq(x)+r(x) where r(x)=0. And this seems like something I would want to try induction on but it seems like a reverse type of induction instead of proving that if n then n+1, I'm doing if n then n1 which I don't really know how to approach. I could try contrapositive induction? If p(x) is not divisible by (xa)n1 where n2 then p(x) is not divisible by (xa)n. I would rewrite it as p(x) not divisible by (xa)n where n1 then p(x) not divisible by (xa)n+1. But how would I even write my induction steps out... I appreciate any insight and help given


Answer



Asserting that p(x) is divisible by (xa)n means that there is a polynomial q(x) such that p(x)=(xa)nq(x). But then p(x)=(xa)n1((xa)q(x)).


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