分解因式m^4-4m^2n^2+n^4
问题描述：
分解因式m^4-4m^2n^2+n^4
答
consider
x^2-4x+1=0
x = 2+√5 or 2-√5
m^4-4m^2n^2+n^4
= (m^2 -(2+√5)n^2). (m^2 -(2-√5)n^2)
答
m^4-4m^2n^2+n^4
=m^2(m^2-4n^2+n^4)
=m^2(m-2n^2)^2