怎样解方程组{2x+y+z=5,x-y+2z=4,3x+2y-3z=3

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怎样解方程组{2x+y+z=5,x-y+2z=4,3x+2y-3z=3
怎样解方程组{2x+y+z=5,x-y+2z=4,3x+2y-3z=3

怎样解方程组{2x+y+z=5,x-y+2z=4,3x+2y-3z=3
2x+y+z=5①
x-y+2z=4②
3x+2y-3z=3 ③
①+②推出3x+3z=9④
②x2+③推出5x+z=11⑤
⑤x3-④推出x=2代入⑤
得z=1,y=0

由2x+y+z=5得出:z=5-2x-y代入x-y+2z=4,得x-y+2(5-2x-y)=4,得y=3-x;
代入z=5-2x-y,得z=2-x;
y=3-x,z=2-x代入3x+2y-3z=3,得x=-1.5

前两个方程相加,得3x+3z=9即x+z=3
2*第二个+第三个,得5x+z=11
联立,得x=2 z=1
随便代入一个方程,得y=0