There is a formula for factoring the "difference of squares." In this case, the answer is (9 - 4x)(9 + 4x)
x2-81=(x-9)(x+9) Factors: x-9, x+9
-9(x + 8)
9y-81=9*(y-9)
9 x 9 = 81 9 squared = 81 3 squared times 3 squared = 81
(a + 3)(a - 3)
7(3y-2)-(-4y+9)
(3 - i)(3 + i)
(9 - 5u)(9 + 5u)
(x + 2)(x - 9)
(7x + 8)(7x - 9)
9(2x - 1)(2x + 1)
(10x-3(10x+3)
(x - 1)(2x - 9)
x2-81 = (x-9)(x+9)
(8x - 3)(8x + 3)
x2 - 6x - 27 = (x-9)(x+3)