Question

Trigonometric substitution
\[\int\limits_{}^{}\frac{ dx }{ \sqrt{x ^{2}-81} },x >9\]

Answer 1

the main thing that i really don't get is the x is greater than 9. There are no example problems in the book that include this so I'm not sure how it works in this situation

Answer 2

Its merely a formality, otherwise you'd be doing complex integration (if x=<9, function has a pole (undefined) or is an imaginary number.

Answer 3

oh i see. I wasn't even thinking about that