For instance, your value for y might also be something like - here, you would get which leads to .
I think what you might need to familiarise yourself with though is the whole concept of . Here, what you've just basically witnessed was the a, which in your case was 1/3, multiplied by 2. And two thirds is...2/3. Which is what you get - and then when you integrate x to that power, you're adding one and getting a coefficient of 3/5.