Answer:
36x^2-49
Step-by-step explanation:
You could remember that (a-b)(a+b) is just a^2-b^2, so you could directly plug in 6x for a, and 7 for b, and get the answer:
36x^2-49
(optional) to show that (a-b)(a+b) is really a^2-b^2, we can distribute using foil:
a^2+ab-ba-b^2
The ab's cancel out, leaving you with: a^2-b^2.
