用因式分解因式分解求x的平方-3mx+2m的平方-mn-n的平方

x^2-3mx+2m^2-mn-n^2
=(x-3m/2)^2-m^2/4-mn-n^2
=(x-3m/2)^2-[m^2/4+mn+n^2]
=(x-3m/2)^2-(m/2+n)^2
若x^2-3mx+2m^2-mn-n^2=0
则 (x-3m/2)^2-(m/2+n)^2=0
x-3m/2=m/2+n
x=2m+n
或x-3m/2=-m/2-n
x=m-n