5xyz-{2x^2y-[3xyz-(4xy^2-x^2y)]} =5xyz-[2x^2y-3xyz+4xy^2-x=xy(8z-x-4y) =2*30=60 看不懂你题目的意思…小括号里4xy2是y追问先化简再求值 (x2y2-4y2)/x2+4xy+4y2)乘（4xy/x-2y+x) 其中x=根号2-1,y=根号2+1
