Multiply the  by the  and get 
Write down all the pairs of factors of its absolute value,
:










Now since the LAST SIGN in 
is MINUS, we SUBTRACT the two 
factors in absolute value:

[Note: If the last term had been PLUS, we 
would have ADDED the two factors in 
absolute value.]










Now we look at the middle term of ,
which is  and we look at the 
list of differences and find the
absolute value of  in the next to
last difference, .

So we substitute  for the 18:




Now we remove the parentheses by distributing:



Factor  out of the first two terms
Factor  out of the last two terms:



Now factor out 



Edwin