The lake and pasture problem solved at last
The Full Problem, Finally Solved Twelve years ago, in 2014, I was helping my girlfriend’s sister with her maths homework. The question was about a farmer with a fixed length of fence trying to enclose the largest possible area against a wall. It had the tidy A-level answer you’d expect, but it planted a question I couldn’t shake: what if the fence could be bent into a circular arc — and what if the wall were a circular lake? I wrote up the in-between version first — an arc of fence against a straight wall, which turns out to be a semicircle — in “A farmer out standing in their field, their field was not mathematics” . Then I took on the lake itself in “The full problem” , carried the differentiation about as far as I could, and stalled on a transcendental equation I couldn’t solve. That post ends with the confession that the tools I needed were not yet in my mathematical toolbox. They are now — though not, strictly speaking, mine. After twelve years I have finally solved i...