[( m n )(2m-n)-2m(m-n)]除于括号二分之一n,

由于:mn/(m+n)=2则有：mn=2(m+n)则:原式=(3m+3n-5mn)/(-m-n+3mn)=[3(m+n)-5mn]/[-(m+n)+3mn]=[3(m+n)-10(m

(m^2-n^2/mn)^2÷(m+n)^2*(m/m-n)^3=(m+n)^2(m-n)^2/m^2n^2÷(m+n)^2*m^3/(m-n)^3=(m-n)^2/m^2n^2*m^3/(m-n)^

3m-5mn+3n/（-m）+3mn-n=【3（m+n）-5mn】/【3mn-（m+n）】=【3-5mn/（m+n）】/【3mn/（m+n）-1】=【3-5x2】/【3x2-1】=-7/5

答：mn/(m+n)=2分子分母同除以mn得：1/(1/n+1/m)=21/m+1/n=1/2(3m-5mn+3n)/(-m+3mn-n)分子分母同除以mn得：=(3/n-5+3/m)/(-1/n+3

mn(m-n)-m(n-m)2=m[n(m-n)-(n-m)2]=m(mn-n2-n2+2mn-m2)=m(3mn-2n2-m2)=-m(m2-3mn+2n2)=-m(m-2n)(m-n)另外m的平方

由于:mn/(m+n)=2则有：mn=2(m+n)则:原式=(3m+3n-5mn)/(-m-n+3mn)=[3(m+n)-5mn]/[-(m+n)+3mn]=[3(m+n)-10(m+n)]/[-(m

因为m-mn=21,mn-n=15,所以：m-n=(m-mn)+(mn-n)=21+15=36m-2mn+n=(m-mn)-(mn-n)=21-15=6希望能都帮到你,追问：对不起啊.我把题发错了,m

-3m^2n/5+m^2n-mn^2=(1-3/5)m^2n-mn^2=(3/5)m²n-mn²2（x-1）-3（2-3x）=2x-2-6+9x=11x-8

原式=（m*m-n*n）+(m*m+mn)=(m+n)(m-n)+m(m+n)=(2m-n)(m+n)

m(m+n)(m-n)-m(m+n)^2=m(m+n)[(m-n)-(m+n)]=m(m+n)(-2n)=-2mn(m+n)=-2*(-1/2)*1=1

m(m-2n)+n(2mn-m^2)=m(m-2n)+n[m(2n-m)]=m(m-2n)(n+1)

先给好平,老是被骗再问：��������再问：����再答：�����再问：������Ҵ

根号(m^3-2m^2n+mn^2)=根号{m(m^2-2mn+n^2}=(n-m)根号mm/(m-n)根号(m^3-2m^2n+mn^2)=m/(m-n)}*(n-m)根号m=-m^(3/2)

原式=(m²+2mn+n²-4mn)(m²-2mn+n²+4mn)+2m²n²=(m²-2mn+n²)(m²+

2m^2-mn-n^2=(m^2-n^2)+(m^2-mn)=(m+n)(m-n)+m(m-n)=(m-n)(m+n+m)=(m-n)(2m+n)再问：x^2+2x-15谢谢再答：x^2+2x-15=

2[mn+(-3m)]-3(2n-mn)=2mn-6m-6n+3mn=5mn-6m-6n=5mn-6(m+n)m+n=2mn=-3=-15-12=-27

3(m^2n+mn)-4(mn-2m^2n)+mn.=3m^2n+3mn-4mn+8m^2n+mn.=11m^2n.

m/(m-n)-n/(m+n)+2mn/(m^2-n^2)=[m(m+n)-n(m-n)+2mn]/(m+n)(m-n)=[m^2+2mn+n^2]/(m+n)(m-n)=(m+n)^2/(m+n)(

先通分,使分母统一为m²-n²,然后化简分子得（m+n）²,再和分母化简得m-n分之m+n.再问：上面的几分之几是个整体，后面的-号是符号，跟前面的不沾边再答：我知道就是