若(3xy+2)+|7-x-y|=0,求代数式（5xy+10y）-[-5x-（4xy-2y+3x）]的值.
问题描述：
若(3xy+2)+|7-x-y|=0,求代数式（5xy+10y）-[-5x-（4xy-2y+3x）]的值.
答
(3xy+2)^2+|7-x-y|=0,则 3xy+2=0,7-x-y=0,即 x+y=7,xy= -2/3 (5xy+10y)-[-5x-(4xy-2y+3x)] =5xy+10y-(-5x-4xy+2y-3x) =5xy+10y+5x+4xy-2y+3x =9xy+8x+8y =9xy+8(x+y) = 9*(-2/3)+8*7 = -6+56 = 50