Question

x - 3y + z = -15
2z + y - z =-2
x + y + 2z = 1
Solve using substitution to find the ordered triple. Help me work through this. I don't know what I'm doing.

Answer 1

@zepdrix @SolomonZelman

Answer 2

are you sue the second equation is typed correctly?
2z + y - z =-2

Answer 3

* 2x + y - z = -2

Answer 4

use eliminationn

Answer 5

I know that

Answer 6

I've worked out most of it but I messed up along the way and can't figure out where I went wrong

Answer 7

so you elimination for the first and second and the second to the third one

Answer 8

That's not how my teacher worked it

Answer 9

well here the real way lol

Answer 10

That doesn't help. I need to actually see the equations being worked

Answer 11

how much do you know?

Answer 12

I don't know what I know? I know I use elimination on the first and second, then first and third, then put those equations together and find the variables from there

Answer 13

http://www.wyzant.com/resources/lessons/math/precalculus/systems_of_equations/substitution_method

Answer 14

Thank you for the link, I'll check it out. But I need someone to work it out with me so I can understand what I'm doing on the test. @wolf1728

Answer 15

Multiply the second equation by -1
x - 3y + z = -15
2x + y - z =-2
x + y + 2z = 1
giving us
x - 3y + z = -15
-2x - y + z =2
x + y + 2z = 1

Now we can add all 3 equations
-3y +4z = -12

Answer 16

My teacher doesn't do it that way. I don't know if he's teaching a different method or what

Answer 17

Okay, how does the teacher do it?

Answer 18

He uses elim. on the first and second equations. Then repeats that on the first and third. Then I add the two new equations to find my variable. Then I plug that variable back into an original equation to find the other two variables

Answer 19

Then I make an ordered triple like (2, 3, 4)

Answer 20

do u want to to solve in matrix?

Answer 21

What does that mean?

Answer 22

shoba - you mean determinants?

Answer 23

pssst seriously google it or watch a youtube video. It's more reliable than us

Answer 24

lol

Answer 25

I don't learn that way. I need. somebody. working. with. meeeeeee...

Answer 26

yeah youtube video work with you step by step

Answer 27

use khan academy

Answer 28

How about solving for x in equation 1 then substituting that value of x in equations 2 and 3?

Answer 29

Because I'm not allowed to do that on the test. I'm in public school and I have 40 something minutes on my test and I have to work my problems out with the method my teacher teaches me with. I can't just decide to change his choice of method

Answer 30

so how u actually want to solve this question?
elimination or substitution

Answer 31

Using elimination on the first and second equations then using that on the first and third?
Anyone know how to do this?

Answer 32

(That's the method babysmith's teacher uses).

Answer 33

yeah i know....
x - 3y + z = -15----1
2x + y -z = 2------2
x + y + 2z = 1------3

1 + 2

x + 2x -3y +y +z - z = -15 +2
3x +4y = -13 -----4

from equation 4----- x = \[\frac{ -4y -13 }{ 3 }\]


the subtitude into equation 1 and 3

\[\frac{ -4y -13 }{ 3 }\] - 3y + z = =-15
\[\frac{ -4y -13 }{ 3 }\] + y +2z = 1

Answer 34

after the subtituition we will get multiply both with 3

(-4y +13/3) + y -z = 2
-4y -13 + 3y -3z = 6
-y -3z = 19--------5

(-4y -13/3) + y + 2z = 1
-4y - 13 + 3y + 6z = 3
-y + 6z =16--------6

equation 5 - 6

-3z -6z = 19 - 16
-3z = 3
z = -1


from equation 5 ----- y =-3z -19 = -3(-1) -16 = -13

from equation 1----- x = -15 + 3y + z = 5 + 3(-13) +(-1) = -55

Answer 35

You don't have to solve it anymore. I can't use that method

Answer 36

CORRECTION TO CALCULATIONS
A) x - 3y + z = -15
B) 2x + y - z =-2
C) x + y + 2z = 1

in equation A solve for X
A) x = 3y -z -15

substitute this into equation B
B) 2 * (3y -z -15) + y -z = -2
B) 6y -2z -30 + y -z = -2
B) 7y -3z =28

substitute this into equation C
C) (3y -z -15) +y + 2z =1
C) 4y +z = 14

Answer 37

my answer is wrong the answer is x = -3,y=4 and z = 0

Answer 38

Yes, I have a calculator here:
http://www.1728.org/unknwn3.htm
the answers are:
X=-3
Y=4
Z=0