It is pi.
In mathematics, pi (π) is a mathematical constant that represents the ratio of a circle's circumference to its diameter. It is an irrational number, meaning it cannot be expressed as a finite decimal or a fraction. The value of pi is approximately 3.14159.
Math uses letters to indicate that specific numbers are not known or as an abbreviation for certain constant.
The letters under the date on some pennies indicates which US Mint branch made the coin. The letter "D" indicates the Denver, Colorado Mint, the letter "S" indicates the San Francisco, California mint and no letter at all indicates the coin was struck at the US Mint in Philadelphia, Pennsylvania.
Until the letter is selected, it is a variable. Immediately after it is selected, the outcome is no longer a variable but a constant.
The letter on the left indicates the month it was made (for instance A=January and B=February). The roman numeral or number on the right indicates the year it was made.
In mathematics, pi (π) is a mathematical constant that represents the ratio of a circle's circumference to its diameter. It is an irrational number, meaning it cannot be expressed as a finite decimal or a fraction. The value of pi is approximately 3.14159.
Words that can be made with the letters in "circumference":CircecremecriercrimecrucifercuecumincurcureecruecumeniceerieemceeemiremuermineerrfeefemurfencefernferricfiefiercerfinfinerfirfirefiremenfirmerfreefreemenfumefunfurIiceifinincurinferinureirememenumeremercuricmicmienmincemineminermireneeniceniecenumericrecurreefreeferrefreferrefiner.ricericerriferimrimeruinrumrumenrunruneuremicuricurineurn
In math and science, Greek alphabet letters are used in formulas to represent various constants and variables. The Greek letter pi is used to represent the ratio of the circumference of a circle to its diameter.
The letter of inquiry.
Because "pi" is the Greek letter for "P" and is used to represent the ratio of a circles diameter to it's circumference. "Pie" just happens to conveniently be the pronunciation of that Greek letters name and a very tasty desert.
Constant Velocity
The letter of inquiry.
Numbers on a phone? OR Time?
Math uses letters to indicate that specific numbers are not known or as an abbreviation for certain constant.
If by permanent you mean constant, you cannot change something that is constant, therefore you cannot add to it (letters or otherwise). It has to be variable. Constant and variable are mutually exclusive terms.
Pi is a letter in the Greek alphabet. Greek letters are used for many mathematical quantities, especially variables in formulas, such as theta for an angular measurement, and of course pi for the ratio of the diameter to the circumference of a circle. Pi notation was first used by the English mathematician William Jones in 1706. The pi notation was used by Euler as early as 1737. Thereafter, pi became the standard notation for this all-important ratio and transcendental constant.
The letters under the date on some pennies indicates which US Mint branch made the coin. The letter "D" indicates the Denver, Colorado Mint, the letter "S" indicates the San Francisco, California mint and no letter at all indicates the coin was struck at the US Mint in Philadelphia, Pennsylvania.