一、用代入法解下列方程组 1、{x+y+z=2,3x-y-4z=5 ,2x+3y-2z=0}二、用加减法解下列方程组1、{2x+3y+z=38,3x+4y+2z=56,4x+5y+z=66}2、{3x+4z=7,2x+3y+z=9,5x-9y+7z=8}只写出哪一题也可以,最好全写
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![一、用代入法解下列方程组 1、{x+y+z=2,3x-y-4z=5 ,2x+3y-2z=0}二、用加减法解下列方程组1、{2x+3y+z=38,3x+4y+2z=56,4x+5y+z=66}2、{3x+4z=7,2x+3y+z=9,5x-9y+7z=8}只写出哪一题也可以,最好全写](/uploads/image/z/978346-10-6.jpg?t=%E4%B8%80%E3%80%81%E7%94%A8%E4%BB%A3%E5%85%A5%E6%B3%95%E8%A7%A3%E4%B8%8B%E5%88%97%E6%96%B9%E7%A8%8B%E7%BB%84+1%E3%80%81%EF%BD%9Bx%2By%2Bz%3D2%2C3x-y-4z%3D5+%2C2x%2B3y-2z%3D0%EF%BD%9D%E4%BA%8C%E3%80%81%E7%94%A8%E5%8A%A0%E5%87%8F%E6%B3%95%E8%A7%A3%E4%B8%8B%E5%88%97%E6%96%B9%E7%A8%8B%E7%BB%841%E3%80%81%EF%BD%9B2x%2B3y%2Bz%3D38%2C3x%2B4y%2B2z%3D56%2C4x%2B5y%2Bz%3D66%EF%BD%9D2%E3%80%81%EF%BD%9B3x%2B4z%3D7%2C2x%2B3y%2Bz%3D9%2C5x-9y%2B7z%3D8%EF%BD%9D%E5%8F%AA%E5%86%99%E5%87%BA%E5%93%AA%E4%B8%80%E9%A2%98%E4%B9%9F%E5%8F%AF%E4%BB%A5%EF%BC%8C%E6%9C%80%E5%A5%BD%E5%85%A8%E5%86%99)
一、用代入法解下列方程组 1、{x+y+z=2,3x-y-4z=5 ,2x+3y-2z=0}二、用加减法解下列方程组1、{2x+3y+z=38,3x+4y+2z=56,4x+5y+z=66}2、{3x+4z=7,2x+3y+z=9,5x-9y+7z=8}只写出哪一题也可以,最好全写
一、用代入法解下列方程组 1、{x+y+z=2,3x-y-4z=5 ,2x+3y-2z=0}
二、用加减法解下列方程组
1、{2x+3y+z=38,3x+4y+2z=56,4x+5y+z=66}
2、{3x+4z=7,2x+3y+z=9,5x-9y+7z=8}
只写出哪一题也可以,最好全写
一、用代入法解下列方程组 1、{x+y+z=2,3x-y-4z=5 ,2x+3y-2z=0}二、用加减法解下列方程组1、{2x+3y+z=38,3x+4y+2z=56,4x+5y+z=66}2、{3x+4z=7,2x+3y+z=9,5x-9y+7z=8}只写出哪一题也可以,最好全写
1.z=38-2x-3y
3x+4y+2(38-2x-3y)=56
-x-2y=-20
x+2y=20
4x+5y+38-2x-3y=66
2x+2y=28
x+y=14
y=14-x
x+2(14-x)=20
-x=-8
x=8
y=6
z=4
2.z=9-2x-3y
3x+4(9-2x-3y)=7
3x+36-8x-12y=7
-5x-12y=-29
5x+12y=29
5x-9y+7(9-2x-3y)=8
5x-9y+63-14x-21y=8
-9x-30y=-55
9x+30y=55
x=1/5(29-12y)
9/5(29-12y)+30y=55
9(29-12y)+150y=275
9*29-108y+150y=275
42y=275-9*29=14
y=1/3
x=1/5(29-4)=5
z=9-10-1=-2
这是初一数学吗?
我就是初一的- -!
1. { x+y+z=2 (1)
{3x-y-4z=5 (2)
{2x+3y-2z=0 (3)
由(1)得,y=2-x-z (4)
把(4)代入(2),得3x-(2-x-z)-4z=5
4x-3z=7 (5)
把(4)代入(3),得2x+3(2-x-z)-2z=0
X+5Z=6 (6),由(6)得X=6-5Z...
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1. { x+y+z=2 (1)
{3x-y-4z=5 (2)
{2x+3y-2z=0 (3)
由(1)得,y=2-x-z (4)
把(4)代入(2),得3x-(2-x-z)-4z=5
4x-3z=7 (5)
把(4)代入(3),得2x+3(2-x-z)-2z=0
X+5Z=6 (6),由(6)得X=6-5Z (7),把(7)代人(5),得
4(6-5Z)-3Z=7,得Z=17/23 则X=6-5*17/23=53/23
Y=-24/23,所以,方程组的解为:
X=53/23
Y=-24/23
Z=17/23
收起
1 题 =89