The square root of 2 is a number used quite a lot in engineering and architecture. The distance between the diagonal corners of a perfect square is equal to the square root of 2 multiplied by the length of one of the sides of the square. The proof of this only requires a knowledge of beginning algebra. If you are interested in the details of the proof, then go here . I only mention it here to show how long ago logic was used to produce useful results.
Negative feedback is an engineering term.
Negative feedback occurs when a physical quantity is measured, and if that quantity should drift from a set value, then mechanisms work to force that quantity back to the set value. For example, a household thermostat which controls the temperature in the house works on the principle of negative feedback. If the temperature in the house should drift below the set value, then the heater starts to operate in order to raise the temperature back to the set value again. Thus, the fact that the temperature is not at the set value causes it to be forced to the set value, and so you get an even set temperature.