已知x的相反数为y-6,y的倒数为2x,求出代数式(5xy+4x+7y)+3(2x-xy)-(4xy-3y)的值 已知x的相反数为y-6,y的倒数为2x,求出代数式(5xy+4x+7y)+3(2x-xy)-(4xy-3y)的值
问题描述：
已知x的相反数为y-6,y的倒数为2x,求出代数式(5xy+4x+7y)+3(2x-xy)-(4xy-3y)的值
已知x的相反数为y-6,y的倒数为2x,求出代数式(5xy+4x+7y)+3(2x-xy)-(4xy-3y)的值
答
x的相反数为y-6则-x=y-6,x=6-y(x+y=6),y的倒数为2x则1/y=2x,2xy=1,
(5xy+4x+7y)+3(2x-xy)-(4xy-3y)化解=-2xy+10y+10y=-2xy+10(x+y)将x+y=6,和xy=1/2带如化解方程，得出原式=59
答
5、已知x的相反数为y-6，y的倒数为2x，求（5xy+4x+7y)+3(2x-xy)-(4xy-3y)的值。
∵-x=y-6,1/y=2x
∴x+y=6,2xy=1
∴ （5xy+4x+7y)+3(2x-xy)-(4xy-3y)
=5xy+4x+7y+6x-3xy-4xy+3y
=-2xy+10(x+y)
=-1+10*6
59
答
x的相反数为y-6,y的倒数为2x
x+y=6 2xy=1
(5xy+4x+7y)+3(2x-xy)-(4xy-3y)
=5xy+4x+7y+6x-3xy-4xy+3y
=-2xy+10x+10y
=10(x+y)-2xy
=60-1
=59