SOLUTION: 2x + 4y + 4z = 16 2x - y + 3z = 9 3x + 4y - z = 8

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Question 475310: 2x + 4y + 4z = 16
2x - y + 3z = 9
3x + 4y - z = 8

Answer by ccs2011(207) About Me  (Show Source):
You can put this solution on YOUR website!
I think the best way to do these is using the elimination method.
Eliminate a variable to break it down into a system of 2 equations, then use elimination again to break it down to a single equation. Solve for that variable and then use substitution to find the 2nd variable in the system of 2 equations. Then substitute both those values into one of the original equations to find 3rd variable.
Let me label each equation: A,B,C for reference
A:2x+%2B+4y+%2B+4z+=+16
B:2x+-+y+%2B+3z+=+9
C:3x+%2B+4y+-+z+=+8
Notice A and C both have a 4y, therefore it will be easiest to eliminate variable y. Multiply C by -1. Add A and C. Call the resulting equation D.
D:-x+%2B+5z+=+8
We still need another equation with x and z. To eliminate y again. Multiply B by 4. Add A and B. Call the resulting equation E.
E:10x+%2B+16z+=+52
Now eliminate x. Multiply D by 10. Add D and E.
66z+=+132
Solve for z. Divide by 66 on both sides.
z+=+2
Substitute z=2 into D.
-x+%2B+5%282%29+=+8
Solve for x.
-x+%2B+10+=+8
Subtract 10 on both sides
-x+=+-2
Flip signs
x+=+2
Substitute x=2, z=2 into B.
2%282%29+-+y+%2B+3%282%29+=+9
Solve for y
4+-+y+%2B+6+=+9
-y+%2B+10+=+9
Subtract 10 on both sides
-y+=+-1
Flip signs
y+=+1
Verify solution by substituting into other equations A and C.
2%282%29+%2B+4%281%29+%2B+4%282%29+=+16
4%2B4%2B8+=+16
16+=+16
True...it works.
3%282%29+%2B+4%281%29+-+2+=+8
6+%2B+4+-+2=+8
8=8
True..it works.
Solution is x = 2, y = 1, z = 2