（3m+n）²-（m+5n）² =(3m+n+m+5n)(3m+n-m-5n)=(4m+6n)(2m-4n)=4(2m+3n)(m-2n)x四次方+4y四次方=x四次方+4y四次方+4x²y²-4x²y²=(x²+2y²)²-4x²y²=(x²+2...