Question

x^2-81
y^2-4a+4
36x^4y^2-169c^2
(x+1)^2-(x-1)^2

Answer 1

1) (x-9)(x+9)

2)(y-2)^2

3)(6x^2y^2-13c)(6x^2y^2+13c)

4)4x