Question

Solve the system of equations. 2x+2y+7z=9, 2x+6y+5z=7, 2x+5y+4z=9. a.z=3 y=-2 z=3 b.x=1 y=0 z=1 c.x=2 y=-1 z=0 d. x=0 y=1 z=2

Answer 1

2x + 2y + 7z = 9.....multiply by -1
2x + 6y + 5z = 7
--------------------
-2x - 2y - 7z = -9 (result of multiplying by -1)
2x + 6y + 5z = 7
-------------------add
4y - 2z = -2

2x + 6y + 5z = 7....multiply by -1
2x + 5y + 4z = 9
-------------------
-2x - 6y - 5z = -7 (result of multiplying by -1)
2x + 5y + 4z = 9
-------------------add
-y - z = 2

4y - 2z = -2
-y - z = 2 ......multiply by -2
-----------------
4y - 2z = -2
2y + 2z = -4 (result of multiplying by -2)
----------------add
6y = -6
y = -6/6
y = -1

4y - 2z = -2
4(-1) - 2z = -2
-4 - 2z = -2
-2z = -2 + 4
-2z = 2
z = -2/2
z = -1

2x + 2y + 7z = 9
2x + 2(-1) + 7(-1) = 9
2x - 2 - 7 = 9
2x - 9 = 9
2x = 9 + 9
2x = 18
x = 18/2
x = 9

solution is : x = 9, y = -1, and z = -1

I am not getting any of ur answer choices....but when I sub my answer choices back into all 3 of the original equations, they come out true