Erik Axel Karlfeldt (1864-1931) was a Swedish poet whose essentially regional, tradition-bound poetry was extremely popular and won him the Nobel Prize in Literature posthumously in 1931; he had refused it in 1918.
... so we add the square of b/(2a) to both 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 ...