I figured this out, this link supplies the details:
http://ocw2.mit.edu/courses/mathemat...0_ChNnotes.pdf
It's a common technique, when presented with (for example) , to make a substitution such as and then we have that the previous integral is equal to . Here is the point I'm concerned about - what allows us to proceed to , as is the common practice? Our limits may not be such that , so what justifies simplifying the square root portion?
I figured this out, this link supplies the details:
http://ocw2.mit.edu/courses/mathemat...0_ChNnotes.pdf