Question

初二分式的加减法：

①x分之3-x分之7+x分之4=_______=________.
②a+2/（a-2）²-4/（2-a）²
③x+a/（x-y）²-a+y/（x-y）²
④1/m-1/n
要有过程

Answer 1

(3)m/m+n+mn/n^2-m^2注：（n^2-m^2可拆成(n-m)*(n+m))=(m*(n-m)+mn)/n^2-m^2=(2mn-m^2)/n^2-m^2=（-2mn+m^2)/（-n^2+m^2）注：这一步是将上一步式子中分子(2mn-m^2）和分母=（m^2-2mn+n^2-n^2）/m^2-n^2(n^2-m^2f)分别乘上-1=(m-n)/m+m-n^2/m^2-n^2（8）（a+b)/a-b-(a-b)/a+b-3ab/(a^2-b^2)=(（a+b)^2-(a-b)^2-3ab)/(a^2-b^2)=(a^2+2ab+b^2-a^2+2ab-b^2-3ab）/(a^2-b^2)=ab/(a^2-b^2)拓展与与运算（9）（a+1)-(a^3/(a^2-a))=（a+1)-(a^2/(a-1))=（（a+1)*(a-1))-a^2）/(a-1))=-1/a-1（10）m/x^2-y^2=(2xy-y^2)/（x^2-y^2）+(x-y)/(x+y)=(m-2xy+y^2)/（x^2-y^2）=(x-y)/(x+y)=(m-2xy+y^2)/（x^2-y^2）=(x-y)(x-y)/(x+y)(x-y)=(m-2xy+y^2)=(x-y)(x-y)=(m-2xy+y^2+x^2-x^2)=(x-y)(x-y)=(m-x^2+(x-y)^2)=(x-y)(x-y)=m-x^2m=x^2纯手打，如果不懂就继续追问

Answer 2

1、原式=-4/x +4/x=0
2、原式
=（a+2)/（a-2)²-4/(a-2)²
=[a+2-4]/(a-2)²
=[a-2]/(a-2)²
=1/(a-2)
3、原式
=（x+a)/(x--y)²-(a+y)/(x-y)²
=(x+a-a-y)/(x-y)²
=(x-y)/(x-y)²
=1/(x-y)
4、原式
=（n-m)/mn