Hiya!
Working on some stupid calculus test and I'm making a very stupid mistake. Unfortunately, I can't find the error (I do know the right way which is to chose the cosine as u but I want to know why my method is wrong as I'll never be smart enough to actually use that).
Let be u, then
So the integral becomes which turns out to be zero, yay! Real answer: 4/3.
My error most likely is at the part where I pick u, but I don't know WHY it is wrong Anyone who can take a minute to explain please?