You have 2 concentric circles of different radius (r for the small circle, R for the big circle), and a tangent to the small circle. You have to find out the pink area. Come up with a general formula for

Well I've read A LOT of bullshit here about a flat Earth. Now I know, I know, most of y'all are trolling the shit out of the idiots who are dumb enough to believe it, but still, you should stop it. So