Expert: Richard J. Raridon - 3/8/2006

Question
Dear Mr.Raridon,
I found this (solved) problem in my textbook:
2x + y - 3z = 1
5x + 2y - 6z = 5
3x + y + 4z= 7
This is a 3x3 system. I tried to solve it (using Gaussian elimination algorithm) and got this solution:
z=0.8 y=-2.6 x=3

But, the textbook said that the solution is:
z=1  y=-2  x=3

Which is correct? Me or the textbook?

Thanks.


Answer
One way to see if you got the correct answers is to put the values back into the original equations.  In this case, neither set of answers is correct, although both sets work for the first two equations.  The answers I got, which check out, are x=3, y=-26/7 and z=3/7.  Are you sure you copied the problem correctly?  The textbook answers would be correct if the last equation were 3x+3y+4z = 7.  I have learned, however, that not every answer given in a book is correct.