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Home Q & A Board Science-Related Homework Help Mathematics
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Ronginah Ronginah
wrote...
Posts: 2
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11 years ago
I know how to use elimination for a pair of equations with 2 variables, but not for 3:

4x + 2y + z = 9
2x - y - z = 2
x + 2y + 3z = 9
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wrote...
#1
11 years ago
4x + 2y + z = 9
2x - y - z = 2
x + 2y + 3z = 9
---------------------
4x + 2y + z = 9
2x - y - z = 2
---------------------
6x + y = 11
---------------------
2x - y - z = 2
x + 2y + 3z = 9
---------------------
(3)2x - y - z = 2
x + 2y + 3z = 9
---------------------
6x - 3y - 3z = 6
x + 2y + 3z = 9
---------------------
7x - y = 15
---------------------
6x + y = 11
7x - y = 15
---------------------
13x = 26
x = 2
---------------------
6x + y = 11
6(2) + y = 11
12 + y = 11
y = 11-12
y = -1
---------------------
2x - y - z = 2
2(2) - (-1) - z = 2
4 + 1 - z = 2
5 - z = 2
-z = 2 - 5
-z = -3
z = 3
---------------------
(2, -1, 3)
wrote...
#2
11 years ago
1) 4x + 2y + z = 9

2) 2x - y - z = 2

3) x + 2y + 3z = 9

Add equation 1 to equation 2

4) 6x + y = 11

Multiply equation 2 by 3 and add the result to equation 2

6x - 3y - 3z = 6
x + 2y + 3z = 9
- - - - - - - - - - -
5) 7x - y = 15
wrote...
#3
11 years ago
6x + y = 11

6x - 3y - 3z = 6
x + 2y + 3z = 9------ADD

7x - y = 15

6x + y = 11
7x - y = 15------ADD

13x = 26
x = 2

12 + y = 11
y = - 1

2 - 2 + 3z = 9
z = 3

x = 2 , y = - 1 , z = 3
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