64A - A^3 = A* ( 64 - A^2) = A * ( 8 - A) * ( 8 + A )
=====================================
X^3 - 10X^2 + 25X = X * ( X^2 - 10X + 25 )
______________________________________
X^2 - 10X + 25
D = 100 - 4*25 = 0
X = 10 : 2 = 5
_______________________________________
X^3 - 10X^2 + 25X = X * ( X - 5) * ( X - 5 )
========================================