when you find the domain, think of x values that cant be plugged in
in this instance, the denominator (bottom) cant be = 0
so x^2-7x-8 =0 this will tell you the #'s you cant use.
(x-8)(x+1) = 0
x=8 and -1
so you domain would be all real numbers such that x doesnt equal 8 or -1