First factor out 



In the parentheses, multiply the first coefficient 4
by the last coefficient 9, getting 36.  Write down
all pairs of integer factors whose product is 36.
They are

1*36
2*18
3*12
4*9
6*6

Since the last sign in the parentheses is +, we
add those:

1+36 = 37
2+18 = 20
3+12 = 15
 4+9 = 13 
 6+6 = 12

Since the middle coefficient of 
is 12, and since 12 = 6+6 we write -12a^2 as -6a^2-6a^2





Factor the first two terms in the parentheses by factoring 
out 


 
Factor the last two terms in the parentheses by factoring 
out 



Inside the outer parentheses take out 
the inner parentheses 



Notice the parenthesis can be written once as squared:



Edwin