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Power Polynomial (Posted on 2019-03-21) Difficulty: 2 of 5
How many integers n>1 are there such that xn-x+a is reducible over the rationals(it can be factored into at least two nontrivial rational factors) for some positive integer a?

No Solution Yet Submitted by Danish Ahmed Khan    
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posible solution Comment 1 of 1
p(x)=x*(xn-1-1)+a    and a integer and a>0

If n is even p(x)>0 for all values of x, and there are no posible roots and the polynomial do not admit real factors (ex: p(x)=x2-x+a: both roots are complex)

Instead is n is odd p(x)>0 for x>=0 and p(x)<0  when |x*(xn-1-1)|>a and (x<0). 

Then: at least one real root (r) exists.

If now we express a in the form of z-zn then the polynomial will have a root for x=z (z is a negative number)

p(x)=(x-z)(axn-1+bxn-2+...+w)      [p(x)=(x-z)*q(x)]
and the coefficients of q(x) will be the potencies of z. 

So the answer should be for n=odd number. 

Ex: 

p(x) x5-x+240

240= -3-(-3)5

p(x)=(x+3)*( x4-3x3+9x2-27x+80)

Edited on March 23, 2019, 9:05 am
  Posted by armando on 2019-03-22 10:14:29

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