# Quick question about a symbol

• Feb 3rd 2010, 04:49 PM
aquajam
What does this symbol mean in mathematics?

Ö

I've been searching but cannot find a definition for it yet.

I was trying to answer this question:

Quote:

Using exactly two 2s and any of the standard mathematical symbols, write down an expression whose value is five.
Solution:
Quote:

Ö.2-2, which shows that two twos can make five!
Is there some trick I'm not seeing?
• Feb 3rd 2010, 04:59 PM
Plato
Quote:

Originally Posted by aquajam
What does this symbol mean in mathematics?
Ö

This is a odd question. All I see is: $\displaystyle \mathop O\limits^{..}$.
I have never seen that use in a standard way.
Your text material should define its use.

A really really old use of $\displaystyle \mathop y\limits^{..}$ is the second derivative of $\displaystyle y$.
• Feb 3rd 2010, 05:08 PM
aquajam
Quote:

Originally Posted by Plato
This is a odd question. All I see is: $\displaystyle \mathop O\limits^{..}$.

That's how it appears in the book. It's a math puzzle book rather than a textbook so it does not elaborate.

An odd typo perhaps? Any ideas how you would solve the question anyway?
• Feb 4th 2010, 12:29 AM
Opalg
Quote:

Originally Posted by aquajam
What does this symbol mean in mathematics?

Ö

I think it's a typo: someone was trying to produce a square root symbol on their keyboard, and it came out as a capital O umlaut. Also, the –2 should be an exponent.

In fact, $\displaystyle \bigl(\sqrt{.2}\bigr)^{-2} = 5$.
• Feb 4th 2010, 08:19 AM
Quacky
Lol, what a funny mistake (Rofl)