分解因式(m^2+n^2)^2-4m^2n^2
解:换元m^2=x n^2=y
=(x+y)^2-4xy
= (x-y)^2
=(m-n)^2(m+n)^2
(m^2+n^2)^2-4m^2n^2
=(m^2+n^2)^2-(2mn)^2
=(m^2+n^2+2mn)(m^2+n^2-2mn)
=(m+n)^2(m-n)^2
用平方差公式
再用完全平方公式
原式=-[(m²+n²)²-4m²n²]
=-(m²+n²+2mn)(m²+n²-2mn)
=-(m+n)²(m-n)²
m^4-4m^2n^2+n^4
=m^2(m^2-4n^2+n^4)
=m^2(m-2n^2)^2
(m^2+n^2)^2-4m^2n^2
=(m^2+n^2+2mn)(m^2+n^2-2mn)
=(m+n)^2(m-n)^2