How to find $x^2 - x$? I'm quite a novice when it comes to maths. I'm on a problem in which I have had to isolate $x$ , through factorials which I completed without problem. However, now I am stuck on a seemingly more minor problem.
The problem I currently have is $x^2 - x = 380$. I know that this can be solved for $x = 20$, however I am unsure how this has been worked out.
I am sorry for this being such a basic question, however I simply have no idea how this was solved.
Thanks,

This particular problem offers another solution angle:  factorization.  We have
$$380=x^2-x=x(x-1)$$
So now we can see that $380$ is a number multiplied by that number less one.  $380$ is between $400=20^2$ and $361=19^2$, so it is reasonable to guess that $x=20$ and it is very easy to see that $20\cdot19=380$, and we are done.
On a separate note, we can also take note that $x^2-x$ is a special form and can be rewritten more compactly in "binomial form" as
$$x^2-x=2{x\choose 2}=380$$
In this form, the binomial series in the quadratic line is the only term, so we can look directly to this series for the answer, which is $x=20$.
