The Excel Slope Function uses the following equation to calculate the slope of the linear regression line through a set of given points:
where the values of x and y are the sample means (the averages) of the known x's and the known y's.The Excel Slope function calculates the slope of the linear regression line through a supplied set of x and y values.
The syntax of the function is:
Where the arguments are as follows:
known_y's    An array known yvalues. 
known_x's    An array of known xvalues. Note that the length of the known_x's array should be the same length as known_y's, and the variance of the known_x's must not be zero. 
The spreadsheet below shows an example of the Excel Slope function used to calculate the slope of the linear regression line through the known_x's and known_y's, in cells F2:F7 and G2:G7.
As shown in cell F9, the Slope function used is:
which gives the result 4.628571429.
Further examples of the Excel Slope function are provided on the Microsoft Office website
If you get an error from the Excel Slope function, this is likely to be one of the following:
#N/A    Occurs if the supplied known_x's and known_y's arrays are of different lengths. 
#DIV/0!    Occurs if either:
