# What is the standard deviation of is sigma(X)=(sigma(Y))/2, what is sigma(X-Y)?

The standard deviation of a defined continuous function is zero (0). $\sigma \left(x - y\right)$ is the sum of the differences between an expected response from a model and the actual data.
$\sigma \left(x - y\right)$ is the sum of the differences between an expected response from a model and the actual data. It is used in the calculation of variance and standard deviations.