Solving for three variables is quite similar to solving for two variables. Just like when solving for two variables, you look for like variables & solve them one-by-one. So, let's get started! :)
Multiply ALL of equation 1 by four.
1) 4(-x - y - z = -8)
Simplify.
1) -4x - 4y - 4z = -32
Both equations 1 & 2 have the same three variables (x, y, z), so, we must look at these equations together.
1) -4x - 4y - 4z = -32 2) -4x + 4y + 5z = 7
Add these equations together, and create a fourth equation.
4) -8x - z = -25
Now, notice how both equations 3 & 4 have the same two variables (x, z).
So, we must look at these equations together.
3) 2x + 2z = 4 4) -8x - z = -25
Multiply ALL of equation 4 by 2.
4) 2(-8x - z = -25)
Simplify.
4) -16x - 2z =-50 3) 2x + 2z = 4
Now, add the equations together, so that we can solve for x.
-14x = -42
Divide both sides by -14.
x = 3
Now, plug in 3 for x into our 3rd equation.
3) 2x + 2z = 4
3) 2(3) + 2z = 4
Simplify.
6 + 2z = 4
Subtract 6 from both sides.
2z = 4 - 6
Simplify.
2z = -2
Divide both sides by 2.
z = -1
Now, plug in -1 for z & 3 for x in our 1st equation.
