jmc

The expression is undefined when the denominator is equal to 0. Thus, we want the sum of the solutions of the equation $2x^2-8x+7=0$. Since for a quadratic with equation $a{x}^2+bx+c=0$, the sum of the solutions is $-b/a$, the sum of the solutions of our equation is $-\frac{-8}{2}=\boxed{4}$.