Factor out the GCF x(3x-1) + 5(3x-1)

*The GCF is 3x-1 so we'll divide both terms by the GCF

x(3x-1) + 5(3x-1)

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3x-1

*cancel the 3x-1 on the x part then the 3x-1 on the 5 part leaving:

x+5

The complete answer then is (3x-1) (x+5)..

I'm confused because where did 3x-1 came from I mean besides the fact that it's the GCF..Is there a rule that states that the "other set of term" will be the GCF???plss help me...