a-1分之a²-a-1
=(a²-a-1)/(a-1)
=(a(a-1)-1)/(a-1)
=a -1/(a-1)
m+2-m-2分之m²
=((m+2)(m-2)-m²)/(m-2)
=(m²-4-m²)/(m-2)
=-4/(m-2)