Question 263387
To determine the domain of any function, we ask 2 questions
(1) is the variable in a square root of any type?
if "yes" set the stuff under the root >= 0 and solve for x.
if "no" go to question 2.
(2) is the variable information in  the denominator?
if "yes" set the denominator stuff not = 0 and solve for x.
if "no" then you say "all reals"
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Using these questions on the given problem., we get
 (1) NO
(2) YES
so 
{{{x-8 = 0}}}
solving for x, we get
 x = 8.
This means we cannot use x = 8 as a domain number.