Thread: Another "theoretical" thing about integrals I have no idea how to do

Question:
If a and b are positive numbers, show that

this(integral (x^a * (1-x)^b) from 0 to 1) = this(http://www.wolframalpha.com/input/?i=integral+(x^b+*+(1-x)^a)+from+0+to+1).

And for this problem, I don't even have the answer in the back of my book! Someone please help!


(Ignore what Wolfram Alpha says - I am just using those links to make it more visual because I don't know how to use latex)

Any help would be GREATLY appreciated!
Thanks in advance!

Let and and you should get:

And since we're dealing with a definite integral, it doesn't matter that we ended up with u's.

Can you please explain why we assume equality of the variables u and x in the last step? Just stating that we can do so because we're dealing with a definite integral doesn't explain it well enough for me.

Since it's a definite integral, you ultimately wind up plugging the limits into the antiderivative. So it doesn't matter if you start with x or u, as whichever variable you use will be replaced by the limits 0 and 1 anyway.

If you aren't buying it, just take your favorite definite integral and change the variable. You should get the same answer.