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Proving a formula

by chocolatelover
Tags: formula, proving
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chocolatelover
#1
Mar2-08, 07:56 PM
P: 239
1. The problem statement, all variables and given/known data
Prove that if p(x)=anx^n +an-1x^n-1+..........a0, where a0,.........., "an" ε reals, is a polynomial, then p can have at most n roots.


2. Relevant equations



3. The attempt at a solution

C ε R is a root of a polynomial p if p(c)=0. If c is a root of p, then x-c is a factor of p.

I'm not sure where to go from here. I think it would probably be the easiest to prove this by proving the contrapositive as being false. Could someone please give me a hint or show me where to go from here?

Thank you very much
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Dick
#2
Mar2-08, 09:45 PM
Sci Advisor
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P: 25,228
Sure. Suppose the polynomial has n+1 different roots. c1,c2,...cn+1. Since c1 is a root the polynomial p(x) can be factored (x-c1)*p1(x) where p1 has degree n-1. The other c's must be roots of p1(x) since they aren't roots of (x-c1). Continue in this way until you reach degree 1. Now you have a linear polynomial with two different roots. Possible?
chocolatelover
#3
Mar2-08, 10:26 PM
P: 239
Thank you very much

Would it be somthing like this?

(p1x)^(n-1)(x-c2)(x-c3)^(n)

Thank you

Dick
#4
Mar2-08, 10:38 PM
Sci Advisor
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P: 25,228
Proving a formula

No, that's not clear at all. Start by proving if n=1 then the polynomial can't have 2 roots. Ok?
chocolatelover
#5
Mar5-08, 10:10 PM
P: 239
Thank you very much

Regards


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