a/b=2/3
a=(2/3)b
(a-b+1)/(a+b-5)
=[(2/3)b-b+1]/[(2/3)b+b-5]
=[1-(1/3)b]/[(5b/3)-5]
分子分母同乘以3
=(3-b)/(5b-15)
=-(b-3)/[5(b-3)]
=-1/5
a/b=2/3
a=(2/3)b
(a-b+1)/(a+b-5)
=[(2/3)b-b+1]/[(2/3)b+b-5]
=[1-(1/3)b]/[(5b/3)-5]
分子分母同乘以3
=(3-b)/(5b-15)
=-(b-3)/[5(b-3)]
=-1/5