How do I find the extinction coefficient of something using the slope of the line of best fit for the graph of its absorbance vs concentration. Basically, we had to find the absorbance and concentration of curcumin at various concentrations and graph them. Then we found the line of best fit, which had a positive slope. The questions asks to calculate the extinction coefficient with this information. I thought that you only needed the absorbance and concentration to find the extinction coefficient. How do I use the slope?