原式=[(m-2n)(m+2n)]²-[(m-2n+m+2n)(m-2n-m-2n)]²
=(m²-4n²)²-(-4mn)²
=m⁴-8m²n²+16n⁴-16m²n²
=m⁴-24m²n²+16n⁴
=16-96+16
=-64