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!