(5m^2+3n^2)^2-(3m^2+5n^2)^2＝（5m^2+3n^2+3m^2+5n^2）（5m^2+3n^2-3m^2-5n^2）＝（8m^2+8n^2）（2m^2-2n^2）＝8（m^2+n^2）2（m^2-n^2）＝16（m^4-n^4）＝16m^4-16n^4
