I'm a little disappointed at the focus here on how it's hard or impossible to visualize when b<a or when either a or b is negative. That's not the point. To m

I'm a little disappointed at the focus here on how it's hard or impossible to visualize when b<a or when either a or b is negative. That's not the point. To me, it's useful to already know that an algebraic proof of that equation exists, but to see it work out visually. I don't need to see it worked out visually for every single possible value for this to be helpful for understanding. It also nicely illustrates how algebra and geometry are linked. And that multiplication is geometrically taking you from 1 dimension to 2.