The ancient Greeks did stuff by example, not using algebra. They said stuff like, "take 22 and multiply by 5..." with actual numbers involved, then at the end they say "and that's how it works in general". So it's up to the reader to generalize from the specific. Algebra works in the opposite direction, where the reader is obliged to specify from the generic. I happen to much prefer the ancient Greek way of doing mathematics, but it seems to have fallen out of fashion.