Unknown (math) facts
In mathematics, an unknown is a number we do not know. In algebra, an unknown is represented by a letter. For example, in the equation E = m c2, the letter m represents an unknown mass, and the letter E represents an unknown amount of energy. Not all letters in algebra represent unknowns. In the example above, c represents a known quantity, the speed of light, which is about 186 thousand miles per second. Because c is so large, the formula E = m c2 tells a person who understands algebra that in an atomic reaction, a small amount of mass can produce a very large amount of energy.
Unknown (math) Facts for Kids. Kiddle Encyclopedia.