Proving Rational Solutions of ax^n + a0 = 0

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SUMMARY

The discussion centers on proving that for a polynomial equation of the form an*x^n + a(n−1)*x^(n−1) + ... + a1*x + a0 = 0, where the coefficients ak are integers, if r = p/q is a rational solution with p and q coprime, then q must divide an and p must divide a0. An example provided illustrates this with the equation x² - 4x + 4 = 0, confirming that 2 is a rational solution, as 2 divides 4 and 1 divides 1. The confusion expressed by participants highlights the importance of understanding the implications of the Rational Root Theorem.

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  • Understanding of polynomial equations and their coefficients.
  • Familiarity with the Rational Root Theorem.
  • Basic knowledge of number theory, specifically coprime integers.
  • Ability to manipulate and solve algebraic equations.
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  • Explore examples of polynomial equations and their rational solutions.
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Homework Statement



Suppose that r is a solution of the equation:

anxn + a(n−1)x(n−1) + . . . + a1x + a0 = 0

where the coefficients ak belongs to Z for k = 0, 1, . . . n, and n is greater or equal to 1. If r is a rational solution r = p/q, where p, q belong to Z and p and q are
coprime, show that q|an and p|a0.


The Attempt at a Solution



Im not even sure where to begin, I am so confused, what am i trying to prove? and how do i prove it, i feel like there is something missing in the question.
 
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cooljosh2k2 said:

Homework Statement



Suppose that r is a solution of the equation:

anxn + a(n−1)x(n−1) + . . . + a1x + a0 = 0

where the coefficients ak belongs to Z for k = 0, 1, . . . n, and n is greater or equal to 1. If r is a rational solution r = p/q, where p, q belong to Z and p and q are
coprime, show that q|an and p|a0.


The Attempt at a Solution



Im not even sure where to begin, I am so confused, what am i trying to prove? and how do i prove it, i feel like there is something missing in the question.

Here's an example to help show you how this works. Here's an equation: x2 - 4x + 4 = 0.

In this equation a2, the coefficient of x2, is 1. a0 is the constant term, and is 4.

If there is a rational number r = p/q that is a solution to this equation, this theorem says that p has to divide a0, and q has to divide a2.

As it turns out, 2 is a solution, and is a rational number - i.e., 2 = 2/1. Clearly 2 divides 4, and 1 divides 1.
 


Thanks i got it now, just got confused with the wording.
 

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