What is a common factor of the equation?

**First** lets look at #9#

The two numbers #-9# and #-9# both have a common factor of #-9#, so we can take out a #-9# by dividing the equation by #-9# and placing it on the outside of the brackets.

**Factoring out -9**

#-9((cancel(-9)a^2)/cancel(-9)+(cancel(-9)a)/cancel(-9))#

New equation: #-9(a^2+a)#

**Now** lets look at #a#

The common factor of #a^2# and #a# is #a#. Take out #a# by dividing the inside of the brackets by #a# and placing it on the outside

**Factoring out the a**

#-9a((a^cancel2)/cancela+cancela/cancela)#

New equation: #-9a(a+1)#

**Note:** Keep in mind that #a/a# is #1#, not zero, because #1/1# is not zero either, so we have to keep a #1# after cancelling out #a/a#.