Where did these symbols come from?

Where did these symbols come from? Like Pi, Fee and this weird E/sideways M and the triangle.

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"Sideways M" is such an epic name for $\Sigma$. – Asaf Karagila Dec 2 '12 at 22:09
On this website you might find some answers: jeff560.tripod.com/mathsym.html – Julian Kuelshammer Dec 2 '12 at 22:31
@AsafKaragila, you are a sensitive and vulnerable man. Women like that. – Will Jagy Dec 3 '12 at 0:11
I don't know about you, but I'm wondering where the name Iydwv Cxscujtdo came from. – 000 Dec 3 '12 at 2:56
@Limitless, it may not be a real name, but he is listed on Area 51 as supporting a very basic site for English as a second language and one for typography, something about one for Greek. So I come to think he arrives at this question honestly, but overestimates the likely amount of help from such sites down the road. – Will Jagy Dec 5 '12 at 1:50

They are Greek letters. The first two you mentioned are Pi ($\pi$) and Phi ($\phi$), respectively (note the spelling). What you refer to as "weird E/sideways M" is the capital letter Sigma ($\Sigma$), and the one that looks like a triangle is the capital letter Delta ($\Delta$). Here is a table of Greek letters and their approximate equivalents, which you may find interesting.

Greek Alphabet

$\begin{array}{l|l} \text{Name} & \text{Capital} & \text{Lowercase} & \text{Equivalent}\\ \hline \text{Alpha*} & \text{A} & \alpha & \text{A} \\ \text{Beta} & \text{B} & \beta & \text{B, V} \\ \text{Gamma} & \Gamma & \gamma & \text{G} \\ \text{Delta} & \Delta & \delta & \text{D} \\ \text{Epsilon*} & \text{E} & \varepsilon,\,\epsilon & \text{E} \\ \text{Zeta} & \text{Z} & \zeta & \text{Z} \\ \text{Eta*} & \text{H} & \eta & \text{Ee} \\ \text{Theta} & \Theta & \theta,\,\vartheta & \text{Th} \\ \text{Iota*} & \text{I} & \iota & \text{I} \\ \text{Kappa} & \text{K} & \kappa & \text{K} \\ \text{Lambda} & \Lambda & \lambda & \text{L} \\ \text{Mu} & \text{M} & \mu & \text{M} \\ \text{Nu} & \text{N} & \nu & \text{N} \\ \text{Xi} & \Xi & \xi & \text{X, Ks} \\ \text{Omicron*} & \text{O} & o & \text{O} \\ \text{Pi} & \Pi & \pi,\,\varpi & \text{P} \\ \text{Rho} & \text{P} & \rho,\,\varrho & \text{R} \\ \text{Sigma} & \Sigma & \sigma,\,\varsigma & \text{S} \\ \text{Tau} & \text{T} & \tau & \text{T} \\ \text{Upsilon*} & \text{Y} & \upsilon & \text{U} \\ \text{Phi} & \Phi & \phi,\,\varphi & \text{F, Ph} \\ \text{Chi} & \text{X} & \chi & \text{Ch, Kh} \\ \text{Psi} & \Psi & \psi & \text{Ps} \\ \text{Omega*} & \Omega & \omega & \text{O} \\ \end{array}$

$\text{*Indicates a vowel}$

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Thanks, but how can I type them? – Iydwv Cxscujtdo Dec 3 '12 at 1:23
@IydwvCxscujtdo You can use $\LaTeX$. For example, $\pi$ will be rendered as $\pi$, and $\Sigma$ will be $\Sigma$. For more information , see MathJax basic tutorial and quick reference. – ctype.h Dec 3 '12 at 1:25
@IydwvCxscujtdo, non $\TeX$ applications (e.g. Microsoft Word, Google Documents) often have 'insert special character' functionality you can use for one-offs rather than having to screw around with learning/installing TeX. – Nick T Dec 3 '12 at 7:58
@IydwvCxscujtdo If you are using Windows, you can also use the Character Map (Start > Accessories > System Tools > Character Map), or by typing Win+R and charmap.exe. This will allow you to enter the characters into programs that do not have an "Insert specail character" function. – ctype.h Dec 3 '12 at 18:39

They are mostly Greek letters that have been adopted because scientists and mathematicians ran out of letters. It also probably has to do with the first real break throughs happening in Greek culture eg. Euclid, Pythagoras, Aristotle.

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One other thing that I would like to add, is that $\Sigma$ is the symbol used in summations. If you don't understand that, just look it up on Google.

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