What Are the Possible Values of the Sum from a 2012-Degree Polynomial Solution?

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The discussion focuses on the polynomial equation $x^{2012}-7x+6=0$ and seeks to determine the possible values of the sum $1+a+a^2+\cdots+a^{2011}$, where $a$ is a root of the polynomial. Participants confirm the correctness of the proposed solutions, indicating a collaborative effort to validate the findings. The analysis of the polynomial's roots and their implications on the geometric series sum is central to the conversation.

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Let $x=a$ be a solution of the equation $x^{2012}-7x+6=0$. Find all the possible values for: $1+a+a^2+\cdots+a^{2011}$.
 
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magneto said:
Let $x=a$ be a solution of the equation $x^{2012}-7x+6=0$. Find all the possible values for: $1+a+a^2+\cdots+a^{2011}$.

My solution:

We're told $x=a$ is a solution of the equation $x^{2012}-7x+6=0$, therefore we have $a^{2012}-7a+6=0$.

It can be rewritten as

$a^{2012}-1-7a+6+1=0$

$a^{2012}-1-7a+7=0$

$(a^{2012}-1)-7(a-1)=0$

$(a-1)(a^{2011}+a^{2010}+\cdots+a+1)-7(a-1)=0$

$(a-1)(a^{2011}+a^{2010}+\cdots+a+1-7)=0$

So the value of the expression $1+a+a^2+\cdots+a^{2011}$ could be either 2012 or 7.
 
anemone said:
My solution:...

Quite clever! (Nod)
 
anemone said:
My solution:

We're told $x=a$ is a solution of the equation $x^{2012}-7x+6=0$, therefore we have $a^{2012}-7a+6=0$.

It can be rewritten as

$a^{2012}-1-7a+6+1=0$

$a^{2012}-1-7a+7=0$

$(a^{2012}-1)-7(a-1)=0$

$(a-1)(a^{2011}+a^{2010}+\cdots+a+1)-7(a-1)=0$

$(a-1)(a^{2011}+a^{2010}+\cdots+a+1-7)=0$

So the value of the expression $1+a+a^2+\cdots+a^{2011}$ could be either 2012 or 7.

Nicely done that's correct.
 

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