how do I find the quadratic function of best fit

Thanks Geno that is great         - it is a pity that it doesn't display the graph as well though  

I'll put this in our 'reference material' sticky thread, with the other useful tool our members have found.   

There is a quadratic regression calculator at this side: http://www.had2know.com/academics/quadratic-regression-calculator.html# 

If you need to calculate this be hand, this site includes the formula.