1893 - Thomas Edison received two U.S. patents. The first was for a "Cut Out for Incandescent Electric Lamps" and another for a "Stop Device" (No. 491,992-3). Also No. 492,150 for "Process of Coating Conductors for Incandescent Lamps."
... 2. (In a field of characteristic 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 ...