解
(1)x²-4x
=x(x-4)
(2)
m²-9
=(m-3)(m+3)
(3)
(x+1)²-16
=[(x+1)-4][(x+1)+4]
=(x-3)(x+5)
(4)
(x-2)²-(x-2)
=(x-2)(x-2-1)
=(x-2)(x-3)