x+5z=7两边同乘以3,减3x-2y=8,
得:2y+15z=16
用上面的方程减2y+3z=8,得:z=5/12
将z=5/12代入x+5z=7 ,得:x=59/12
将z=5/12代入2y+3z=8,得:y=27/4