# Correlation Coefficient and Determination Coefficient

I'm really new to linear regression and am trying to teach myself.

In my textbook there's a problem that asks why R^2 in the regression of Y on X = the sample correlation between X and Y the whole squared.

I've been throwing my head against this for a while and I keep getting stuck because in the correlation coefficient there is a X and X bar term, whilst in the R2 term there is no such thing.

Can anyone provide a derivation as to why R2 = correlation coeff squared?

Thanks!

-
It might help if you define the terms in your question. What is the equation for $R^2$, in particular? –  Rahul May 10 '12 at 9:27
If by $R^2$ you mean the "explained variance", then stats.SE might be a more suitable site for this question. See, for example, this question or this one for some ideas related to this. –  Dilip Sarwate Jan 4 '13 at 23:46