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,

A somewhat different way of putting this is that if you know that $x=20$ is a solution to $x^2-x=380$ then that implies that you can write
$$x^2-x-380 = 0 \Leftrightarrow (x-20) f(x) =0,$$
for some function $f$.  In this case $f(x)=x+19$ so the other value of $x$ that makes $x^2-x-380$ equal to zero is $x=-19$.
