Factor
\left(r-4\right)\left(r^{2}+9\right)
Evaluate
\left(r-4\right)\left(r^{2}+9\right)
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r^{2}\left(r-4\right)+9\left(r-4\right)
Do the grouping r^{3}-4r^{2}+9r-36=\left(r^{3}-4r^{2}\right)+\left(9r-36\right), and factor out r^{2} in the first and 9 in the second group.
\left(r-4\right)\left(r^{2}+9\right)
Factor out common term r-4 by using distributive property. Polynomial r^{2}+9 is not factored since it does not have any rational roots.
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