Question

Use the substitution method to solve the following system of equations.

x + 2y – z = 7
4x – y + 3z = –2
2x + 2y – z = 9

Answer 1

Well, here we go:

First let's set the first equation equal to:

– z = 7 - x - 2y
Which becomes:
z = x+2y - 7 okay?

Answer 2

Yes

Answer 3

No put this in equation #2:

4x – y + 3z = –2
Becomes:

4x – y + 3(x+2y - 7) = –2
Which becomes:

4x - y +3x +2y -21 = -2

Answer 4

With me so far?

Answer 5

Yes kinda

Answer 6

So, then we combine like terms to get:

4x - y +3x +2y -21 = -2
7x + y -21 = -2
y = -7x +19

And finally put this in the third equation and solve for x.

So put in the first and second equations into the third one and solve for x.

Answer 7

Im not sure

Answer 8

So we have z = x+2y - 7 and we have y = -7x +19

SO in the third equation:
2x + 2y – z = 9

Wherver you see a z, put that equation, and where you see a y, put in the equation for y. (First put in the y in the z equation)

Answer 9

I got it! thanks!!

Answer 10

No problem kiddo.