how to write infinity

I wanted to ask this question in the 0.999... thread but it was locked. How do you write "infinity" mathematicially? I only thought you might write it with the line over the countinuing numbers.

"In mathematics, the repeating decimal 0.999… which may also be written as 0.\bar{9} , 0.\dot{9} or 0.(9)\,\! denotes a real number equal to one." http://en.wikipedia.org/wiki/0.99999

Anybody has a clue? You cant trust wiki!

 

i thought ∞ was the accepted mathimatical symbol to denote an infinite number of terms etc.

 

thats not what im talking about, read it again.

 

8 on the side is the mathematical way to write it...

 

You need to draw a bar over the top of the recurring sequence, or a dot on top of the first and last in the sequence.

 

what itza said. You need to put a dot above the infinite number.

 

ok, but according to wikipedia (who sucks, havent checked the sources though), ... is also allowed, is it?

And please stop posting without reading the whole post and its sources...

 

I use 0.(9) for it and I'm sure it's an acceptable way. Dots are often used, but I'm not sure they are technically proper way.

 

they arent, there'd be no clear way to indicate what part is repeating

 

Like the wiki says, all the ellipse really means when used in that context is that "Some infinite portion was left unstated".

But like Ijffdrie said, it's not a good idea to use it because it lacks clarity, and can be misunderstood.

 

ijffdrie I agree, and thats why i got a bit choched to see that on wikipedia (not the first time though).

 

For plain text, 0.(9) is probably the most clear and unambiguous. If possible, I draw a bar over the repeating digits. The dots are also acceptable.

Most professional mathematicians would never need write it out in that format anyway. For repeating decimals there is always a ratio that represents it concisely; for 0.(3) it would be 1/3, for 0.(9) it would be 9/9 or, more likely, 1.

 

What about 0,654(321)?

 

That's a valid representation. You have used the decimal comma instead of the decimal point, but both are accepted.

If you want to know the reduced ratio that results in that decimal, it is 217889/333000. Plug it into a calculator to verify if you want.

 

Ahh, no jocking today? I just found it worying that there is no clear one cut way of doing it. I myself use a bar over the diggits that are repeating, easist and most pro looking. Just wanted to know your opinions!