十字相乘法.
（m+n)(m-2n)x²+(5m²+2mn-12n²)x+2m(3m+6n)=0
m+n 3m+6n
m-2n 2m
十字相乘,2m*(m+n)+(3m+6n)*(m-2n)=2m^2+2nm+3m^2-12n^2=5m^2+2mn-12n^2
故方程分解为:
[(m+n)x+(3m+6n)][(m-2n)x+2m]=0
x1=-3(m+2n)/(m+n)
x2=-2m/(m-2n)
解方程：(m²-mn-2n²)x²+(5m²+2mn-12n²)x+6
十字相乘法.
（m+n)(m-2n)x²+(5m²+2mn-12n²)x+2m(3m+6n)=0
m+n 3m+6n
m-2n 2m
十字相乘,2m*(m+n)+(3m+6n)*(m-2n)=2m^2+2nm+3m^2-12n^2=5m^2+2mn-12n^2
故方程分解为:
[(m+n)x+(3m+6n)][(m-2n)x+2m]=0
x1=-3(m+2n)/(m+n)
x2=-2m/(m-2n)