-1/4x^4+9y²=-(x/2+3y)(x/2-3y) x²-(x-y)²=(x+x-y)(x-x+y)=(2x-y)y 已知4m+n=90,2m－3n＝10, (m＋2n)²－(3m－n)²=(m＋2n+3m－n)(m＋2n-3m+n)=(4m+n)(-2m+3n)=90×(-10)=-900 -1/4x²y&...4x²-(x-y)4x²-(x-y)不能分解因式，可以是少了个平方。这道题是正规教参上的题目吗？4x²-(x-y)²前面已写了两遍再复制粘贴一遍x²-(x-y)²=(x+x-y)(x-x+y)=(2x-y)y