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

The values are x = 8 and x = -1.

To find the undefined values, we need to know when the denominator is zero.
To do this, we need to factor it and find the value that would make either factor equal to zero.

If factors to: (x - 8)(x + 1)

Therefore, the undefined values would be at 8 and -1.