Work Step by Step
Using the Factor Theorem, if $x=a$ is a factor, then $(x-a)$ is a factor of $f(x)$. Hence here $f(x)=(x+1)(x-2)(x-4)=(x+1)(x^2-2x-4x+8)=(x+1)(x^2-6x+8)=x^3-6x^2+8x+x^2-6x+8=x^3-5x^2+2x+8$
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