This is a list of divisions of the United States Army past and present. Armored, cavalry, and infantry are each numbered in their own sequences, and are thus grouped; the airborne and mountain divisions are numbered with the other infantry.
... 2, the element 2a is zero and it is impossible to divide by it.)
The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in the formula should be understood as ...