This spreadsheet demonstrates the calculation of the slopes of secants to a non-linear function which approximate the slope of a tangent at a given point on the curve of the function. The function used here is [math]f(x)=1/x[/math]. The secants are through the points [math]A[/math] and [math]B[/math]. Point [math]A[/math] is a fixed point at [math](0.5,2)[/math] and point [math]B[/math] starts at [math](1,1)[/math] and keeps moving closer to [math]A[/math] until it reaches [math]B(0.501,1.99601)[/math]. The [i]rises[/i] and [i]runs[/i] are calculated for each set of points and the slope is then calculated between [math]A[/math] and [math]B[/math]. As we see, the slope of the tangent between [math]A(0.5,2)[/math] and [math]B(0.501,1.99601)[/math] equals [math]-0.399202[/math]. We can make the reasonable conclusion that the slope of the tangent to this function at [math]A[/math] equals [math]-4[/math].