What is the sum of all values of $y$ for which the expression $\frac{y+6}{y^2-5y+4}$ is undefined?
The expression (y + 6)/(y^2 - 5y + 4) is undefined when y^2 - 5y + 4 = 0. By the quadratic formula, the roots are 3 - sqrt(5) and 3 + sqrt(5), and their sum is 6.
+501 
