I may be missing something here, but it seems like the answer solution is a little off. In the second set of equations they use to eliminate x we are given the following:

4y - 2x + 10z = -34
-y - 2x + 5z = 100

5y + 5z = 134.

Wouldn't combining these two equations give 3y - 4x + 15z = 66?

I'm referring to the top of page 135 in the blue algebra book. Any help would be much appreciated.

Thanks!

Rob

Here is a solution:

x - 3y - 10z = 67
-x +2y + 5z = -17
-2x - y + 5z = 100

add the first two equations:

-y - 5z = 50

multiply first equation by 2 and add it to the third:

-7y - 15z = 234


multiply 4th equation above by -7 and add it to the last equation above

20z = - 116

z = -29/5

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