How Do You Apply Trigonometric Substitution to Integrate Sqrt(X^2 + 9)?

[cooltee13]

Homework Statement

Evaluate the Integral: Sqrt[(X^2)+9]

Homework Equations

I know its an Integration By parts problem, but I don't know how to start it.

The Attempt at a Solution

Im JUST learning this as I type this problem out, I've just been stuck on it for a while and my book does a horrible job of explaining how to do problems. If anybody could explain the Trigonometric substitution technique or knows of a good website that explains it I would be very grateful.

For this problem though, all I did was set x=3sin(u) and dx=3cos(u).

I don't know if that's right though, because like I said, I just "learned" this yesterday

 

[Vid]

When the terms are added, you do a tan sub.

http://tutorial.math.lamar.edu/Classes/CalcII/TrigSubstitutions.aspx