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."
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Note that when computing roots numerically, the usual form of the quadratic formula is not ideal. See Loss of significance for details.
Derivation
The ...