24x^2 + 20x - 84

36x^2-4x-40

9a^2-1

-show work

explain a little.

1. 4 (2x-3) (3x+7)

2. 4 (9x-10) (x+1)

3. (3a+1) (3a-1)

Step-by-step explanation:

1. Add and subtract the second term to the expression and factor by grouping.

2. Same thing for #2 (look at #1)

3. Since both terms are perfect squares, factor using the difference of squares formula a^ (2) - b^ (2) = (a+b) (a-b) where a = 3a and b = 1