1.
(1)x-2y+z=9
(2)2x+y+3z=10(两边×2)得(5)
(3)3x+2y-4z=-3(与(1)相加得(4)
(4)4x-3z=6(两边×5,得(8)
(5)4x+2y+6z=20(与(1)相减)得(6)
(6)5x+7z=29(两边×4)得(7)
(7)20x+28z=116
(8)20x-15z=30(与(7)相减
43z=86
z=86/43=2(代入到(4)
4x=6+3z=6+3*2=12
x=12/4=3
把x=3;z=2代入到(1)
2y=x+z-9=3+2-9=-4
y=-4/2=-2
验算:
(1)3-2*(-2)+2=9
(2)2*3-2+3*2=10
(3)3*3+2*(-2)-4*2=-3
2.
(1)y=2x-7把(1)代入到(2)得(4)
(2)5x+3y+2z=2
(3)3x-4z=4
(4)5x+3(2x-7)+2z=2
5x+6x-21+2z=2
11x+2z=23(两边×2;得(5)
(5)22x+4z=46与(3)相加
25x=50
x=50/25=2代入到(1)
y=2x-7=2*2-7=-3
4z=3x-4=3*2-4=2
z=2/4=1/2
验算:
(1)-3=2*2-7=-3
(2)5*2+3*(-3)+2*1/2=2
(3)3*2-4*1/2=4
3.
(1)x-4y+z=-3(与(2)相加得(4)
(2)2x+y-z=18
(3)x-y-z=7(与(1)相加得(5)
(4)3x-3y=15(两边÷3)得(6)
(6)x-y=5(两边×2得(7)
(7)2x-2y=10(与(5)相减)
(5)2x-5y=4
3y=6
y=6/3=2代入到(6)
x=5+y=5+2=7
z=x-y-7=7-2-7=-2
验算:
(1)7-4*2+(-2)=7-8-2=-3
(2)2*7+2-(-2)=18
(3)7-2-(-2)=7