Now, look at the last term of our trinomial: - 45
and our middle coefficient: -4
All we need to do is figure out what signs to put in this
to give BOTH the -45 and the -4...
It can't be
because this would give us a POSITIVE 45.
For the same reason, it can't be
We need to use a + and a - ...
and we need a -4 ...
Check it with FOIL!