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The same question was posed here Find the value of a+b+c but I cannot make sense of the answer.

My long division must be incorrect as I ended up with $a+b+c$ which is definitely wrong. I added $0$ to represent $x^3$ and $x^1$ terms.

I know the remainder should be zero if $x+1$ is a factor.

I am not putting two and two together.

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    $\begingroup$ If $x+1$ is a factor then $x=-1$ is a root. @user554754 can you finish? $\endgroup$ – Minz Apr 26 '18 at 3:30
  • $\begingroup$ You have to put $ signs around your MathJax for it to be formatted. $\endgroup$ – saulspatz Apr 26 '18 at 3:31
  • $\begingroup$ In fact, if a definite answer exists, only one answer i spossible $\endgroup$ – Hagen von Eitzen Apr 26 '18 at 3:37
  • $\begingroup$ Your result is $ax^4+bx^2+c=(\cdots)\cdot(x+1)+\color{red}{a+b+c}$ and you know that it should be $ax^4+bx^2+c=(\cdots)\cdot(x+1)+\color{red}{0}$ and the question asks for the value of $a+b+c$. The rest is really like puting two and two together $\endgroup$ – Hagen von Eitzen Apr 26 '18 at 3:40
  • $\begingroup$ I added a few details to the linked question. $\endgroup$ – Ross Millikan Apr 26 '18 at 3:43
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$x = -1$ is a root of polynomial
put $x = -1$ in $a x^4 + b x^2 + c$
$a + b + c = 0$

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