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