Fatore:
a) x²-81
b)4x²-36
c)4x²-12xy+9y²
(x-9) . (x+9)
(2x-6) . (2x+6)
(2x -3y).(2x-3y)
x2=81
x=9
4x2=36
x2=36/4
x2=9
x=3
4x²-12xy+9y² = (2x - 3Y)²