不解方程组,2x+y=-8,x-3y=2 求7y(x-3y)^2-2(3y-x)^3的值

显示全部楼层 · 2013-5-30 21:26:15

2x+y=-8,x-3y=2 7y(x-3y)^2-2(3y-x)^3=7y(x-3y)^2+2(x-3y)^3=(x-3y)2(7y+2x-6y)=22×(-8)=-32...

千问 · 2013-5-30 21:26:15

7y(x-3y)^2-2(3y-x)^3=7y(x-3y)2+2(x-3y)3=(x-3y)2[7y+2(x-3y)]=(x-3y)2(2x+y)∵2x+y=-8,x-3y=2∴原式=22×（-8）=-32...

千问 · 2013-5-30 21:26:15

因为X-3Y=2所以3Y-X=-2原式=7Y*2^-2(3Y-X)^3
=7Y*4-2*(-2)^3
=28Y+16
=28(-8-2X)+16
=28[-8-(-8-Y)] 代换就好了...

千问 · 2013-5-30 21:26:15

7y(x-3y)^2-2(3y-x)^3=7y(x-3y)^2+2(x-3y)^3=(x-3y)2(7y+2x-6y)=22×(-8)=-32...