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**DivideBy0** After I complete $\displaystyle \int \frac{\sqrt{x^2-9}}{3}\,dx$ by sec substitution I get

$\displaystyle 3\sec^{-1}\left(\frac{x}{3}\right)-\sqrt{x^2-3}+C$.

But this doesn't match the calculator's answer:

$\displaystyle 3\tan^{-1}\left(\frac{\sqrt{x^2-9}}{3}\right) - \sqrt{x^2-3}+C$

After differentiating the result my answer is different as well... I thought the answers we got would be equivalent though...

Then the second question is $\displaystyle f(x) = 3$. Find the equation.