Is there a math symbol for right(-angled) triangle?

Cannot find one, all triangle symbols are equilateral triangles.

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If you have access to Unicode fonts there is U+2BBF (⊿) RIGHT TRIANGLE

Otherwise, picture mode to the rescue:

\documentclass{article}

\usepackage{amsmath}
\def\lr{\mbox{\begin{picture}(7,10)
\put(1,0){\line(1,0){5}}
\put(1,0){\line(1,2){5}}
\put(6,0){\line(0,1){10}}
\end{picture}
}}

\def\ll{\mbox{\begin{picture}(7,10)
\put(1,0){\line(1,0){5}}
\put(6,0){\line(-1,2){5}}
\put(1,0){\line(0,1){10}}
\end{picture}
}}
\begin{document}

\begin{align}
A &= \ll\\
B &= \lr
\end{align}

\end{document}

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I have, but need my Latex source to be portable. Will this solution work with say majority of Latex installations? –  Daniel Langr Aug 1 '12 at 14:04
no, probably not (or it would work on the installation but you'd have to train the human to invoke xelatex rather than latex or something). If you want it portable you could just draw a small triangle in picture mode and use it as a symbol. –  David Carlisle Aug 1 '12 at 14:52
There is also Lower right triangle ◿, Lower Left Triangle ◺ and Triangular Ruler 📐. (Credits to Shapecatcher) –  canaaerus Aug 1 '12 at 18:19