已知2x+y=6,x-3y=1,求7y(x-3y)-2(3y-x)的值.
问题描述:
已知2x+y=6,x-3y=1,求7y(x-3y)-2(3y-x)的值.
答
7y(x-3y)^2-2(3y-x)^3 =7y(x-3y)^2 +2(x-3y)^3 ={7y+2(x-3y)}(x-3y)^2 =(2x+y)(x-3y)^2 =6x1^2 =6