# Math Help - Quick question about a symbol

1. ## Quick question about a symbol

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:

Using exactly two 2s and any of the standard mathematical symbols, write down an expression whose value is five.
Solution:
Ö.2-2, which shows that two twos can make five!
Is there some trick I'm not seeing?

2. Originally Posted by aquajam
What does this symbol mean in mathematics?
Ö
This is a odd question. All I see is: $\mathop O\limits^{..}$.
I have never seen that use in a standard way.
Your text material should define its use.

A really really old use of $\mathop y\limits^{..}$ is the second derivative of $y$.

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

4. 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, $\bigl(\sqrt{.2}\bigr)^{-2} = 5$.

5. Lol, what a funny mistake