Note: Australia is generally considered to be a continental landmass, rather than an island. If however one does count Australia among the islands it, not Greenland, would be the largest in the world (unless one also considered Antarctica an island).
... details.
Derivation
The quadratic formula is derived by the method of completing the square[?].
<math>ax^2+bx+c=0</math>
Dividing our quadratic ...