where to find this symbol

I have tried to create a triangle (by the polygon tool) and would like to delete only the line at the bottom of the triangle. How to do it ?

The only thing I know about this symbol is its mathematical definition : "the empty word", but I don't know where to find it in the symbols.

Do you know the name of the symbol? If you do, you can look it up to see if it’s available in any installed fonts. Symbols are provided by fonts installed in the operating system, not by individual applications such as Illustrator.

If you must draw it, it can help to have the grid visible, and Snap to Grid enabled. Then you can quickly draw it with a few quick clicks of the Pen tool. See demo below.

But it would be best to locate it in a font, because then it can use proper scaling with type hints, and metrics.

I would carefully take a photo of a caterpillar and then do some live trace in Illustrator with low quality settings.

Look in the Glyphs panel using a Symbol font or an Opentype font with a large character set, like Arial Unicode. If you know the name of the symbol (I do not) then you could search for it in Apple’s Emoji & Symbol viewer (Keyboard menu in menubar or press Command-Control-Space.

In case I would like to create it with illustrator, how to do it. I have tried to do the top of this symbol with two lines, but I don't know how to determine an angle between the two lines.

Install a math font.

Mylenium