一,18xy ²-x³y³=xy²(18-x²y)二.25-x² =(5+x)(5-x)三.-x^4+9x²y²=9x²y²-x^4=x²(9y²-x²)=x²(3y+x)(3y-x)四.am+bn+2m+3n=m(a+2)+n(b+3) 此式只...