# Quick question about finding standard deviation

by rock.freak667
Tags: deviation, solved, standard
 HW Helper P: 6,204 Now I know that $$\sigma=\sqrt{var(x)}$$ which simplifies to this expression : $$\sigma=\sqrt{\frac{1}{N}\sum_{i=1}^{N}(x-\overline{x})^2}$$ can someone show me how they got such an expression? and in chemistry I have to use a standard deviation calculation to get out a problem. Now normally I would use the above equation but my notes tell me to use this equation: $$\sigma=\sqrt{\frac{1}{N-1}\sum_{i=1}^{N}(x-\overline{x})^2}$$ Which one is correct to use? and can someone tell me if this is correct $$c_v =\frac{\sigma}{\overline{x}}$$ where $$c_v$$ is the coefficient of variation