Factor
\left(a-4\right)\left(a+b\right)
Evaluate
\left(a-4\right)\left(a+b\right)
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a\left(a-4\right)+b\left(a-4\right)
Do the grouping a^{2}-4b+ab-4a=\left(a^{2}-4a\right)+\left(ab-4b\right), and factor out a in the first and b in the second group.
\left(a-4\right)\left(a+b\right)
Factor out common term a-4 by using distributive property.
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