Question

HELP! how to solve system of equations
x-2y+z=-1
y+2z=-4
x+y+3z=-5

what do we do when there is a missing variable??? :(

Answer 1

what are you solving for??

Answer 2

x,y, and z

Answer 3

I'm not sure what to do since the x is missing.

Answer 4

Write the system as:

x - 2y +z =-1
0x +y+ 2z=-4
x + y + 3z = -5

In the first and third equations, eliminate the variable x.
Then, you will have a system of 2 by 2 equations in the unknowns y and z.

Of those two equations, eliminate a variable and solve for the other.

If you are allowed to use technology, take a look at the online 3 x 3 linear equation system solver at:
http://math.bd.psu.edu/~jpp4/finitemath/3x3solver.html

@mathcalculus

Answer 5

Question?

Answer 6

thank you

Answer 7

im trying to solve it step by step

Answer 8

x - 2y +z =-1
0x +y+ 2z=-4
x + y + 3z = -5


x - 2y +z =-1 x - 2y +z =-1
x + y + 3z = -5 --multiply through by -1 -> -x - y - 3z = 5
----------------
-3y - 2z = 4

Answer 9

ok

Answer 10

i got a little lost. now i know why

Answer 11

i got that, so what about the second equation?

Answer 12

@mathcalculus

Your Task:

Solve this system - Just add them.

-3y - 2z = 4
y+ 2z=-4
-----------------

Answer 13

it bothers me that the 0x is there.

Answer 14

Don't look at it.
When I eliminated the "x" in equations #1 and #3, the 0x was not an issue.

Answer 15

i got this: -2y=0

Answer 16

but it can't be. it's undefined.

Answer 17

Note that here:

Solve this system - Just add them.

-3y - 2z = 4
y+ 2z=-4
-----------------

I excluded the 0x term. It is just a placeholder of sorts.

Answer 18

0/2?

Answer 19

yeah i know.

Answer 20

-2y = 0
y= 0/2
y = 0-->

You have division by 0 and division into 0 mixed up.

Answer 21

so y is 0?

Answer 22

okay i got that step right.

Answer 23

z=2

Answer 24

x=-6

Answer 25

it's wrong... :(

Answer 26

It is wrong. But, unless you show your steps, I cannot help you find the error.

Answer 27

z=-2

Answer 28

ok hold on.

Answer 29

i got it right! x=1 y=0 z=-2 ! =]

Answer 30

thanks so much! i really aprreciate it!

Answer 31

You are welcome.