Old Math Puzzle

If you like riddles, here’s one. Maybe you’ll solve it right away, or maybe you’ll stare at the screen stupidly for 10 minutes before scrolling down to see if anyone put the answer in the comments, not because you want to see the answer but because you want to see the beginning of the answer, so you’ll know that once you figure it out you’ll at least have a place to check to make sure you’re right. But then you’ll read not only the full answer, immediately, but enough debate among the commenters to make you question whether you’d ever have figured it out in the first place. “You.” I solved it right away.