2 2 (a - x) *(x + a)
(a - x)^2*(x + a)^2
1*(a + x)*(a - x)
(1*(a + x))*(a - x)
4 4 2 2 a + x - 2*a *x
a^4 + x^4 - 2*a^2*x^2
2 2 (a + x) *(x - a)
(a + x)^2*(x - a)^2
(a + x)^2*(a - x)^2