I was working on some limit homework and everything was going fine until I reached this problem:
$\lim_{\Delta x \to 0} \frac{2(x + \Delta x) - 2x}{\Delta x}.$
I am understanding limits but the triangle (delta?) before the x is throwing me off. I have never seen it used this way before and I have no idea what it means in this context. Could anyone help me out? Thanks.