# Find b so that x - 1 is a factor

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• March 6th 2010, 07:33 AM
nandokommando
Find b so that x - 1 is a factor
Find b so that x - 1 is a factor of x^5 + x^4 + x^3 + x^2 + b.

The answer is -4, I just don't know how to get there. Can anyone give me a step by step?
• March 6th 2010, 07:59 AM
e^(i*pi)
Quote:

Originally Posted by nandokommando
Find b so that $x - 1$ is a factor of $x^5 + x^4 + x^3 + x^2 + b$.

The answer is -4, I just don't know how to get there. Can anyone give me a step by step?

Use the factor theorem which is stated below

$(x-k)$ is a factor of the polynomial $p(x)$ if and only if $p(k) = 0$

For your example $f(1) = 0$. To find f(1) substitute 1 wherever you see x in your equation