Question:

Factor 4x²- 36

Answer:

This is the difference of two squares. Such an expression is factored this way:

(2x + 6) (2x - 6)

As usual, I advise you to check it by multiplying it out, and you'll see it's right. If you use the F.O.I.L. method of multiplying these expressions together, you'll see this is

4x² - 12x + 12x - 36

Do you see how the "outer" and "inner" cancel (the "O" and "I" of F.O.I.L.) each other out?