In the Midst of a meadow well stor'd with Grass
I took up an Acre to tether my Ass
How long must ye Cord be that feeding all round
He mayn't grase more nor less than his acre of Ground
By thinking in terms of acres, Washington was preparing for an early career in surveying. He certainly had learned enough Euclidean geometry to know all radii of the same circle are equal.
(The problem was printed in The compleat measurer: or, The whole art of measuring, by William Hawney, 2nd ed. 1721, p. 288.)