a/b=c/d两边加上氏并核1a/b+1=c/d+1(a+b)/b=(c+d)/歼掘c (1)a/b=c/d两边减蔽梁去1a/b-1=c/d-1(a-b)/b=(c-d)/c则b/(a-b)=c/(c-d) (2)(1)×(2)(a+b)/(a-b)=(c+d)/(c-d)