Question 76656
To multiply this, you have to FOIL which means First Outer Inner Last
Here's how it goes:

First 4m^2
Outer 12mn
Inner -12mn
Last -9n^2
 Combine like terms and you get the answer
4m^2+12mn-12mn-9n^2

4m^2-9n^2

That method is for multiplying any two binomials together, If you have two binomials that are the same except for the sign in the middle, you can just multiply the First and Last terms and still get the same answer. As you can see, the middle two terms are subtracted out.