Although much of the practical work in HCI revolves around the design of graphical user interfaces, HCI is concerned with a number of topics, including
... 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 a perfect square; it ...