x的3M次方=4,y的3n次方=5,＝＝＞,y的n次方=5^(1/3)
(x的2m次方)的立方+(y的n次方)的立方-x的2m次方×y的n次方×x的4m次方×Y的n次方
=x的6M次方+y的3n次方﹣x的6M次方×y的2n次方
=16+5﹣16×5^(2/3)
=21﹣46.78
=﹣25.78