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**Second derivative.....**

## Homework Statement

Okay, this is a rough one for me. It was a question I got on my test, and (obviouslly) didnt get right. Im studying all my old exams for my final in 2 days and this is the last of the problems that I cant wrap my head around....any help would be greatly appreciated.

[tex]

\frac{d^2}{dx^2} \int_0^{x}\,(\Big\,\int_1^{sint}\sqrt{1+u^2}\,du)\Big\,dt

[/tex]

I know, through the fundamental theorem of calculus that I can just replace (so to speak) the 't' in 'sint' to a 'sinx'. and then replace the [itex]u^2[/itex] with 'sinx'. I think thats it for the first part, then I think to find the second derivative I just derive it again? I dunno...Im seriously lost; all those parenthesis and variable changes are throwing me off. Im not necessarily looking for an answer (although that would definately help), moreso just looking for some direction. Thanks in advance.