①ac分之2bc ②xy²分之（x+y）y ③（x+y）²分之x²+xy ④（x-y）²分之x²-y²

①ac分之2bc ②xy²分之（x+y）y ③（x+y）²分之x²+xy ④（x-y）²分之x²-y²

①2b/a
②（x+y)/xy
③x/(x+y)
④(x+y)/(x-y)

1=a分之2b 2=xy分之x+y 3=（x+y）²分之x（x+y）=x+y分之x 4=（x-y）²分之（x+y）（x-y)=x-y分之x+y

①ac分之2bc
2bc/ac=2b/a
②xy²分之（x+y）y
(x+y)y/xy^2=（xy+y^2）/(xy^2)=1/y+1/x
③（x+y）²分之x²+xy
(x^2+xy)/(x+y)^2=[x(x+y)]/（x+y）^2=x/(x+y)
④（x-y）²分之x²-y²...

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①ac分之2bc
2bc/ac=2b/a
②xy²分之（x+y）y
(x+y)y/xy^2=（xy+y^2）/(xy^2)=1/y+1/x
③（x+y）²分之x²+xy
(x^2+xy)/(x+y)^2=[x(x+y)]/（x+y）^2=x/(x+y)
④（x-y）²分之x²-y²
(x^2-y^2)/（x-y）^2=(x-y)(x+y)/（x-y）^2=(x+y)/(x-y)

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1. 2bc/ac=2b/a
2. y(x y)/xy^2=(x y)/xy
3. (x^2 xy)/(x y)^2=x(x y)/(x y)^2=x/x y
4. (x^2-y^2)/(x-y)^2=(x y)(x-y)

④（x-y）²分之x²-y²
（x-y）*（x-y）=x²*（-2xy)*y²