Question

Find the domain of f(x)=x-9/x squared-81

Answer 1

`f(x)=(x-9)/(x^2-81)\\\\\text{The domain:}\\\\x^2-81\\eq0\qquad\text{add 81 to both sides}\\\\x^2\\eq81\to x\\eq\pm√(81)\\\\x\\eq-9\ \wedge\ x\\eq9\\\\Answer:\ \boxed{\text{All real numbers except -9 and 9}}\to\boxed{x\in\mathbb{R}-\{-9,\ 9\}}`