已知2x+2y-4z=0,2x+4y+5z=0,求x+y+z/x-y+z的值

问题描述:

已知2x+2y-4z=0,2x+4y+5z=0,求x+y+z/x-y+z的值

本题不一定要算出x、y,也能解出.
(1)2x+2y-4z=0
(2)2x+4y+5z=0
(2)-(1):2y+9z=0 即2y=-9z
(1)÷2可得:x+y =2z
故x+y+z=3z
则x-y+z=(x+y+z)-2y=3z+9z=12z
易得x+y+z/x-y+z=3z/12z=1/4