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Equal Sign

The equals sign or equality sign (=) is a mathematical symbol used to indicate equality. It was invented in 1557 by Robert Recorde. In an equation, the equals sign is placed between two expressions that have the same value.

What is an equal sign (=)?

The equal sign (=) is the mathematical symbol for equality. Invented by 16th century Welsh physician Robert Recorde, who also brought the plus sign (+) to the English. The sign appears between two mathematical units that amount to the same value:

  • 4 + 2 = 6
  • 12 × 3 = 36
  • 98 – 47 = 51
  • 75 ÷ 5 = 15

Recorde first used the symbol in his 1557 book The Whetstone of Witte. The two parallel, horizontal lines of the equal sign—which were originally much longer than in modern-day usage—were chosen because they represent identical entities. About two centuries had passed before the symbol gained universal acceptance; the earlier æ symbol was used throughout much of Europe into the 18th century. Alternately, Recorde's symbol was spelled with vertical lines (||) for a time.

The word "equal" derives from aequalis, the Latin word for "uniform."

Examples of use

The following different uses can be made of the equal sign in mathematics:

  • Statements of fact: x = 8
  • Creations of definition: let x = 9
  • Conditional statements: if x = 7, then…
  • Universal equivalence: 4 × 3 = 6 + 6

Early math students sometimes wind up using the equal sign incorrectly by attempting to demonstrate equal values in an unorthodox manner. For instance, if someone was looking for the sum of 2, 3, 6, 9, and 12, the argument might look like this:

  • 2 + 3 = 5 + 6 = 11 + 9 = 20 + 12 = 32

Technically, this would be an attempt at saying the following:

  • ([(2 + 3 = 5) + 6 = 11] + 9 = 20) + 12 = 32

Trouble is, the first notation won't work due to the differing value of each equality, which would actually be stating the following if taken to its conclusion:

  • 5 = 11 = 20 = 32 = 32

For the initial argument to work, it would need to be written like this:

  • 2 + 3 = 5, 5 + 6 = 11, 11 + 9 = 20, 20 + 12 = 32

Other uses of the equal sign (=)

The equal sign first appeared in computer code during the mid 1950s with the program FORTRAN I, in which the sign was used to assign value. For instance, when x = 3, the number 3 represents the value of x. Though similar to mathematical usages of the equal sign, the programming here follows a slightly different rule, because the value placed after the sign is the first to be evaluated, and may in fact relate to a prior x value. For instance, an assignment that reads x = x + 5 would up the x value by 5. This usage, as well as that of ALGOL—a competing program that also debuted in the late '50s—have remained in use into the millennium.

The equal sign has been put to unorthodox use among select individuals with double-barreled names who have applied it in lieu of hyphens. A notable example was 1900s Brazilian aviation pioneer Alberto Santos=Dumont, whose double-surname featured an equal sign in the middle; he applied the sign as a show of equal respect to the ethnicities of his mother (Brazilian) and father (French). Some people in Japan are also known to use the equal sign as a name separator.

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