Prepositions and postpositions, together called adpositions, are a class of words that express spatial or temporal relations (in, under, towards, before) or marking various semantic roles (of, for). A preposition or postposition typically combines with a noun or pronoun, or more generally a noun phrase, this being called its complement, or sometimes object. A preposition comes before its complement; a postposition comes after its complement. English has prepositions rather than postpositions – words such as in, under and of precede their objects, as in in England, under the table, of Jane. Some...

In mathematics, Euler's identity (also known as Euler's equation) is the equality where e is Euler's number, the base of natural logarithms, i is the imaginary unit, which satisfies i2 = −1, and π is pi, the ratio of the circumference of a circle to its diameter. Euler's identity is named after the Swiss mathematician Leonhard Euler. It is considered an example of mathematical beauty. == ExplanationEdit == Euler's identity is a special case of Euler's formula from complex analysis, which states that for any real number x, where the values of the trigonometric functions sine and cosine are given...