1) x^2 - 121 = (x + 11)(x - 11)
2)81 - a^2 = (9 - a)(9 + a)
3) 9m^2 - 4n^2 = (3m - 2n)(3m + 2n)
4) 64a^2 - 9b^2 = (8a - 3b)(8a+3b)
5) 36m^2 - 25b^2 = (6m - 5b)(6m + 5b)
6)x^2 -25 = (x- 5)(x+5)
7) t^2 - 4 = (t - 2)(t + 2)
8) 4m^2 -1 = (2m - 1)(2m +1)
9) 16x^2 - 25 = (4x - 5)(4x + 5)
10) 25x^2 - 144 = (5x - 12)(5x + 12)