# clairification on standard deviation

I have a homework question that gives me a set of $x$ values and their respective $f(x)$ values and asks me to find the line which best fits the data. I have to do this by finding the estimated progression line. I did it and wasn't too satisfied with the result, and I remembered the teacher said to ignore points that are 3 times greater than the SD(stnandard deviation).

I looked up how to do SD, but found only examples using single values, how do I calculate it for pairs of values like $x$ and $f(x)$, or do I just look at $f(x)$?

-
just look at $f(x)$ –  jay-sun Nov 13 '12 at 0:37
Ok, thanks alot! –  rex Nov 13 '12 at 1:00