How can I calculate the standard error of the slope manually if I don't want to use Excel's functions?

Manually calculating the standard error of the slope involves several steps: calculating the residuals, the sum of squared residuals (SSE), the sum of squared deviations of x from its mean (SSX), and the degrees of freedom (n-2). The formula is: SE(slope) = SQRT(SSE / SSX * 1/(n-2)). This is complex and prone to errors compared to using Excel's built-in tools like LINEST or the Regression analysis.