m²+4m+4分m²-4除m+2分m-2
=（m+2)^2分之（m+2）（m-2）除m+2分m-2
=（m+2）分之（m-2）除m+2分m-2
=1
(a²-2a)除a分a-2
=a（a-2）除a分a-2
=a（a-2）*（a-2）分之a
=a^2