[Math] Where did these symbols come from

Question

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

Answer 1

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} $

$\text{*Indicates a vowel}$