X+Y+Z=15 X+5Y+10Z=70
问题描述：
X+Y+Z=15 X+5Y+10Z=70
求X,Y和Z
答
两式相加10X+5Y+Z+X+Y+Z=70+15 11X+6Y+2Z=85 两式相减(10X+5Y+Z)-(X+Y+Z)=70-15 9X+4Y=65 所得两式相减(11X+6Y+2Z)-(9X+4Y)=85-65 2X+2Y=20 X+Y=10 代入X+Y+Z=15,所以Z=5 把Z=5代入10X+5Y+Z=70,得10X+5Y+5=70,10X+5Y...