Question

For what values of x is the rational expression below undefined? x-7/x^2-7x-8

Answer 1

We have

f(x)=(x-7)/(x²-7x-8)

resolving the quadratic equation
using a graph tool-------- > see the attached figure
x=-1  x=8
therefore
(x-7)/(x²-7x-8)=(x-7)/[(x+1)*(x-8)

the answer is  -1  and  8