-2(x-3y)-{6x-【5x+y-3(3x-4y)】-2x-3(5x-4y）｝,其中x=-2,y=-3,先化简再求代数式的值

题目

-2(x-3y)-{6x-【5x+y-3(3x-4y)】-2x-3(5x-4y）｝,其中x=-2,y=-3,先化简再求代数式的值

答案

-2(x-3y)-{6x-【5x+y-3(3x-4y)】-2x-3(5x-4y）｝=-2x+6y-{6x-[5x+y-9x+12y]-2x-15x+12y}=-2x+6y-{-11x+12y-(-4x+13y)}=-2x+6y-(-7x-y)=-2x+6y+7x+y=5x+7y当x=-2,y=-3时原式=-10-21=-31