First cirumnavigation of the globe by a ship of Ferdinand Magellan's expedition. Only one ship survived the journey, under the command of the Basque captain Sebastian Elkano (1522).
... sides, getting
<math>x^2+\frac{b}{a}x+\frac{b^2}{4a^2}=-\frac{c}{a}+\frac{b^2}{4a^2}.</math>
The left side is now a perfect square; it is the square of (x ...