接下列方程组 1.x+y=7,y+z=8,x+z=9,2.5x+y+z=6,x+5y+z=-2,x+y+5z=10
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接下列方程组 1.x+y=7,y+z=8,x+z=9,2.5x+y+z=6,x+5y+z=-2,x+y+5z=10
1.
(1)x+y=7
(2) y+z=8
(3) x+z=9
(1)式等于:x=7-y代入到(3)得(4)
(4)(7-y)+z=9
-y+z=2与(2)相加
y+z=8
2z=10
z=5代入到(2)得
y=3代入到(1)得
x=4
2.
(1)5x+y+z=6
(2) x+5y+z=-2
(3) x+y+5z=10
(2)(3)相减得(4)
-4y+4z=12(同时÷4)得(4)
(4)-y+z=3
(2)式两边×5得(5)
(5)5x+25y+5z=-10与(1)相减得(6)
(1)5x+y+z=6
(6)24y+4z=-16(两边同时÷4)
6y+z=-4与(4)相减
-y+z=3
7y=-7
y=-1代入到(4)
z=2(把y=-1,z=2代入到(1)式得
5x=6-2+1=5
x=1
(1)x+y=7
(2) y+z=8
(3) x+z=9
(1)式等于:x=7-y代入到(3)得(4)
(4)(7-y)+z=9
-y+z=2与(2)相加
y+z=8
2z=10
z=5代入到(2)得
y=3代入到(1)得
x=4
2.
(1)5x+y+z=6
(2) x+5y+z=-2
(3) x+y+5z=10
(2)(3)相减得(4)
-4y+4z=12(同时÷4)得(4)
(4)-y+z=3
(2)式两边×5得(5)
(5)5x+25y+5z=-10与(1)相减得(6)
(1)5x+y+z=6
(6)24y+4z=-16(两边同时÷4)
6y+z=-4与(4)相减
-y+z=3
7y=-7
y=-1代入到(4)
z=2(把y=-1,z=2代入到(1)式得
5x=6-2+1=5
x=1
(x+y-z)(x-y+z)=
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