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