What does 2+2=

Well Firstly what is "2":

2 (two) is a number, numeral, and glyph. It is the natural number following 1 and preceding 3.

In Mathematics
Two has many properties in mathematics.[1] An integer is called even if it is divisible by 2. For integers written in a numeral system based on an even number, such as decimal and hexadecimal, divisibility by 2 is easily tested by merely looking at the one's place digit. If it is even, then the whole number is even. In particular, when written in the decimal system, all multiples of 2 will end in 0, 2, 4, 6, or 8.

Two is the smallest and the first prime number, and the only even one (for this reason it is sometimes humorously called "the oddest prime"). The next prime is three. Two and three are the only two consecutive prime numbers. 2 is the first Sophie Germain prime, the first factorial prime, the first Lucas prime, and the first Smarandache-Wellin prime. It is an Eisenstein prime with no imaginary part and real part of the form 3n − 1. It is also a Stern prime, a Pell number, and a Markov number, appearing in infinitely many solutions to the Markov Diophantine equation involving odd-indexed Pell numbers.

It is the third Fibonacci number, and the third and fifth Perrin numbers.

Despite being a prime, two is also a highly composite number, because it has more divisors than the number one. The next highly composite number is four.

Vulgar fractions with 2 or 5 in the denominator do not yield infinite decimal expansions, as is the case with most primes, because 2 and 5 are factors of ten, the decimal base.

Two is the base of the simplest numeral system in which natural numbers can be written concisely, being the length of the number a logarithm of the value of the number (whereas in base 1 the length of the number is the value of the number itself); the binary system is used in computers.

For any number x:

x+x = 2·x addition to multiplication
x·x = x2 multiplication to exponentiation
xx = x↑↑2 exponentiation to tetration
Two also has the unique property that 2+2 = 2·2 = 2²=2↑↑2=2↑↑↑2, and so on, no matter how high the operation is.

Two is the only number x such that the sum of the reciprocals of the powers of x equals itself.

Powers of two are central to the concept of Mersenne primes, and important to computer science. Two is the first Mersenne prime exponent.

Taking the square root of a number is such a common mathematical operation, that the spot on the root sign where the exponent would normally be written for cubic roots and other such roots, is left blank for square roots, as it is considered tacit.

The square root of two was the first known irrational number.

The smallest field has two elements.

In the set-theoretical construction of the natural numbers, 2 is identified with the set . This latter set is important in category theory: it is a subobject classifier in the category of sets.

Two is a primorial, as well as its own factorial. Two often occurs in numerical sequences, such as the Fibonacci number sequence, but not quite as often as one does. Two is also a Motzkin number, a Bell number, an all-Harshad number, a meandric number, a semi-meandric number, and an open meandric number.

Two is the number of n-Queens Problem solutions for n = 4. With one exception, all known solutions to Znám's problem start with 2.

Evolution of the Glyph
The glyph we use today in the Western world to represent the number 2 traces its roots back to the Brahmin Indians, who wrote 2 as two horizontal lines (it is still written that way in modern Chinese and Japanese). The Gupta rotated the two lines 45 degrees, making them diagonal, and sometimes also made the top line shorter and made its bottom end curve towards the center of the bottom line. Apparently for speed, the Nagari started making the top line more like a curve and connecting to the bottom line. The Ghubar Arabs made the bottom line completely vertical, and now the glyph looked like a dotless closing question mark. Restoring the bottom line to its original horizontal position, but keeping the top line as a curve that connects to the bottom line leads to our modern glyph.

In Science
The number of polynucleotide strands in a DNA double helix.
The first magic number.[3]
The atomic number of helium.
Group 2 in the Periodic table of the elements consists of the alkaline earth metals whose usual valence is +2.
Period 2 in the Periodic table consists of the eight elements lithium through neon.

Astronomy
Messier object M2, a magnitude 6.5 globular cluster in the constellation Aquarius.
The New General Catalogue object NGC 2, a magnitude 14.2 spiral galaxy in the constellation Pegasus
The Saros number of the solar eclipse series which began on May 4, 2861 BC and ended on June 21, 1563 BC . The duration of Saros series 2 was 1298.1 years, and it contained 73 solar eclipses.
The Saros number of the lunar eclipse series which began on February 21, 2541 BC and ended on April 22, 1225 BC. The duration of Saros series 2 was 1316.2 years, and it contained 74 lunar eclipses.
The Roman numeral II stands for bright giant in the Yerkes spectral classification scheme.
The Roman numeral II (usually) stands for the second-discovered satellite of a planet or minor planet (e.g. Pluto II or (87) Sylvia II Remus)
A binary star is a stellar system consisting of two stars orbiting around their center of mass.

In Technology
The resin identification code used in recycling to identify high-density polyethylene.

In Religion
The Ten Commandments were given in the form of two tablets (Shnei Luchot HaBrit)
Two candles are traditionally kindled to usher in the Shabbat, recalling the two different ways Shabbat is referred to in the two times the Ten Commandments are recorded in the Torah. These two expressions are known in Hebrew as שמור וזכור ("guard" and "remember"), as in "Guard the Shabbat day to sanctify it" (Deut. 5:12) and "Remember the Shabbat day to sanctify it" (Ex. 20:8)
Two challahs (lechem mishnah) are placed on the table for each Shabbat meal and a blessing made over them, to commemorate the double portion of manna which fell in the desert every Friday to cover that day's meals and the Shabbat meals
In Jewish law, the testimony of two witnesses are required to verify and validate events, such as marriage, divorce, and a crime that warrants capital punishment
Rosh Hashana, the first day of the Jewish year, is a 2-day holiday
"Second-Day Yom Tov" (Yom Tov Sheini Shebegaliyot) is a rabbinical enactment that mandates a two-day celebration for each of the one-day Jewish festivals (i.e., the first and seventh day of Passover, the day of Shavuot, the first day of Sukkot, and the day of Shemini Atzeret) outside the land of Israel
Animals boarded Noah's Ark two by two.

In Culture
The most common philosophical dichotomy is perhaps the one of good and evil, but there are many others. See dualism for an overview. In Hegelian dialectic, the process of synthesis creates two perspectives from one.

Two (二, èr) is a good number in Chinese culture. There is a Chinese saying "good things come in pairs". It is common to use double symbols in product brandnames, e.g. double happiness, double coin, double elephants etc. Cantonese people like the number two because it sounds the same as the word "easy" (易) in Cantonese.

In Finland, two candles are lit on Independence Day. Putting them on the windowsill invokes the symbolical meaning of division, and thus independence.[citation needed]

In pre-1972 Indonesian and Malay orthography, 2 was shorthand for the reduplication that forms plurals: orang "person", orang-orang or orang2 "people".[citation needed]

In North American educational systems, the number 2.00 denotes a grade-point average of "C," which in some colleges and universities is the minimum required for good academic standing at the undergraduate level.[4]

In Astrology, Taurus is the second sign of the Zodiac.

In Other Feilds
Groups of two:

Lists of pairs
list of twins
The name of several fictional characters: Number Two.
The designation of the Trans-Canada Highway in most of the province of New Brunswick.
U.S. Route 2, two separated highways in the northern tier of the United States, the western segment connecting Everett, Washington to St. Ignace, Michigan and the eastern route connecting Rouses Point, New York to Houlton, Maine.
The lowest channel of television in the United States, Canada, and Mexico on which television signals are broadcast.

Next what is the "plus" symbol:

The plus and minus signs (+ and −) are mathematical symbols used to represent the notions of positive and negative as well as the operations of addition and subtraction. Their use has been extended to many other meanings, more or less analogous. Plus and minus are Latin terms meaning "more" and "less", respectively.

History
Though the signs now seem as familiar as the alphabet or the Hindu-Arabic numerals, they are not of great antiquity. The Egyptian hieroglyphic sign for addition, for example, resembled a pair of legs walking in the direction in which the text was written (Egyptian was written in boustrophedon, or alternating directions), with the reverse sign indicating subtraction.
In Europe in the early 15th century the letters P and M were generally used.

The earliest print appearance of the modern signs seems to come from a book on Behende und hüpsche Rechenung auff allen Kauffmanschafft or Mercantile Arithmetic by Johannes Widmann in 1489, used to indicate surpluses and deficits. The + is a simplification of the Latin "et" (comparable to the ampersand &). The − may be derived from a tilde written over m when used to indicate subtraction; or it may come from a shorthand version of the letter m itself. Widmann referred to the symbols − and + as minus and mer: "was − ist, das ist minus, und das + ist das mer".[1]

According to the Earliest Uses of Various Mathematical Symbols website, a book published by Henricus Grammateus in 1518 is the earliest found to use + and − for addition and subtraction.

Robert Recorde, the designer of the equals sign, introduced plus and minus to the UK in 1557 in The Whetstone of Witte:

" There be other 2 signes in often use of which the first is made thus + and betokeneth more: the other is thus made – and betokeneth lesse. "

Plus Sign
The plus sign is a binary operator that indicates addition, as in 2 + 3 = 5. It can also serve as a unary operator that leaves its operand unchanged (+5 means the same as 5). This notation may be used when it is desired to emphasise the positiveness of a number, especially when contrasting with the negative (+5 versus −5).

The plus sign can also indicate many other operations, depending on the mathematical system under consideration. Many algebraic structures have some operation which is called, or equivalent to, addition. Moreover, the symbolism has been extended to very different operations. Plus can mean:

exclusive or (usually written ⊕): 1 + 1 = 0, 1 + 0 = 1
logical disjunction (usually written ∨): 1 + 1 = 1, 1 + 0 = 1
concatenation of strings is sometimes written: "a" + "b" = "ab", although this usage is questioned by some for violating commutativity, a property addition is expected to have.
In grading systems (such as examination marks), the plus sign indicates a grade one level higher; for example, B+ ("B plus") is one grade higher than B. Sometimes this is extended to two plus signs; for example B++ is one grade higher than B+.

In C and some other computer programming languages, two plus signs indicate the increment operator; for example, x++ means "increment the value of x by one". By extension, "++" is sometimes used in computing terminology to signify an improvement, as in the name of the language C++.

Plus and minus signs are often used in tree view on a computer screen to show if a folder is collapsed or not.


[edit] Alternative plus sign
A Jewish tradition that dated from at least from the 19th century was to write plus using a symbol like an inverted T. This practice was then adopted into Israeli schools (this practice goes back to at least the 1940s[2]) and is still commonplace today in some elementary schools (including secular schools) while fewer secondary schools.[3]. It is also used occasionally in books by religious authors, but most books for adults use the international symbol "+". The usual explanation for the origins of this practice is that it avoided the writing of a symbol "+" that looked like a Christian cross[3]. Unicode has this symbol at position U+FB29 "Hebrew letter alternative plus sign"

In closing, 2 + 2 = 4

=)

From: http://en.wikipedia.org/