I'm not sure if anyone every answered this question for you, but the reason why the equation was disappearing is that Microsoft Word uses a Unicode Character to represent this value. In Microsoft's RichTextBox Control, they have normalized support for RichEdit v.1 which only supports TEXT and RTF formats. This means that your text form only supports characters in the range of 0-255. The square root character that is generated in Word is probably either an image or a unicode based character. Why is this important? Because the first time you use the following syntax:

VB Code:
  1. Dim t as string

  2. t = Richtextbox1.Text

Any Unicode values would be flattend and images would be dropped. Since there is not value in the 0-255 character set that covers a square root symbol (unless you use a font like symbol, but then, there is only a square root marker because the font has mapped the glyph to the character), you're pretty much out of luck here if you want to design something using VB's Richtextbox since the first time you save or manipulate the results, the data will be lost.

The only way to get around this limitation is to use a Unicode enabled control (like the Forms 2.0 Object -- though you cannot redistribute it), create you're own RichEdit Control, which is time consuming, but I've found to be the best solution (in terms of reusablity) or use a combination of bit and mnemonic representations to show how your program works.