Question

解方程组3x+y+z=6,x+3y+z=5,x+y+3z=9

Answer 1

3x+y+z=6

x+3y+z=5

x+y+3z=9

全加起来,得

3x+y+z+x+3y+z+x+y+3z=6+5+9

5x+5y+5z=20

x+y+z=4

3x+y+z-(x+y+z)=6-4

2x=2,x=1

同理将2、3式减x+y+z=4

得y=0.5,z=2.5