Expert: Richard J. Raridon - 10/14/2008

Question
i do dont understand how to do this.
here is the problem. if any one can help me i thank you.

-6x+2y+12z=-90
-4x+y+4z+-40
-3z=15



the other problem im having truble with is this one.

6x+6y-2z=-410
-2x-y-3z=182
x+6y+6z=-335


If any one can help me i thank you so much because i need it and dont get this

Answer
1. you know that z=-5 so put that into the first two equations
-6x+2y-60 = -90
-4x+y-20 = -40
So now you have two equations, two unknowns and can easily solve to get x=5 and y=0
2. 6x+6y-2z = -410
multiply 2nd eq. by 6 to get -12x-6y-18z = 1092
add those together to get -6x-20z = 682
Add that 2nd eq. to the third one to get
-11x-12z = 757
So you again have two equations, two unknowns and can get
x= -47, y=-28 and z = -20