Solve the following system of equation for y.
2x - y = 13
2x = y
I came up with no solution for y.
The book's answer is y = -39.
Who's right?
It would appear that, in this case, you are right.
Because if $\displaystyle 2x=y$ and then we substitute for $\displaystyle y$ in the othe equation we get $\displaystyle 2x-2x=13
$ I don't think so! because $\displaystyle 2x-2x=0\neq13$
Are you sure you copied the problem down right?
You could also substitute $\displaystyle -39$ for $\displaystyle y$wherever it occurs in both equations. You will find that
$\displaystyle 2x-(-39)=1$
$\displaystyle 2x+39=13$
$\displaystyle 2x=-26$
$\displaystyle x=-13$
and now for the other equation
$\displaystyle 2x=-39$
$\displaystyle x=\frac{-39}{2}$
and since the coordinates $\displaystyle (\frac{-39}{2},-39)\neq(-13,-39)$there is no solution.
So, you got a bad book baby!