Rewrite
Let
Now, see what the antiderivative is?.
#2: Solve your equation for x in terms of y and integrate from 0 to 5.
do you mean you haven't done it in class, or you're just not good at it. in either case, look it up in your textbook. once you figure out what to substitute, it's pretty much the regular substitution technique. back-substituting can be somewhat annoying, but it is not that bad, and it can be avoided altogether with definite integrals as you see here.
so let's start you off:
we wish to evaluate
Let
Change our limits to avoid back-substitution:
when ,
when ,
So our integral becomes:
Now continue