4m²n²-(m²+n²)²=4m²n²-（m^4+2m²n²+n^4)=4m²n²-m^4-2m^2n^2-n^4=-m^4+2m^2n^2-n^4=-(m^4-2m^2n^2+n^4)=-(m^2-n^2)^2^2就代表平方,以此类推^4就代表4次方...保证对？当然