# Thread: Draw a Tangent in Microsoft Excel graph

1. Member
Join Date
Jan 2012
Posts
17

## Draw a Tangent in Microsoft Excel graph

I need help to get a tangent line in Microsoft Excel. There is no option given in the settings of graph in excel. Is there any other way to do that.

2. Member
Join Date
Jul 2011
Posts
441

## Re: Draw a Tangent in Microsoft Excel graph

There is no built in functionality for this. You could use the (AutoShape) drawing tool and draw a line, but that's not very satisfying. Or you could determine the slope at the desired point, compute the endpoints of the line with the calculated slope intersecting at the desired point, and add ax XY series to the chart using these endpoints.

3. Member
Join Date
Jul 2011
Posts
435

## Re: Draw a Tangent in Microsoft Excel graph

I am assuming that you need this result for the school. Then I would not make such a great idea and spend hours with Excel. I would print out the chart, read off as large as possible, i.e. on an A4 sheet of paper and then manually create a tangent and its slope from the intersections with the axes. Is fast and sufficiently accurate. If you really want to try it in Excel: I know of no way to provide only a portion of the graph with a trend line. As a remedy, I would then only a diagram of the relevant part (i.e., the linear increase) and let them draw then create a linear trend line.

4. Member
Join Date
Aug 2011
Posts
461

## Re: Draw a Tangent in Microsoft Excel graph

The function describes a saturation kinetics. The formula is known. Can you adjust the parameters of the formula with the method of least squares sum leave (goes through the Solver in Excel). Based on the formula and the fitted parameter, you can easily calculate the initial slope. Then a pair of points is sufficient to draw the line through the origin of Excel with this slope can be. This is not just then some approximate arbitrary line that arbitrarily on any of lying on a straight points under consideration is based, but the best line that uses all available data and is based on the model of saturation kinetics.

5. Member
Join Date
Aug 2011
Posts
565

## Re: Draw a Tangent in Microsoft Excel graph

The tangent to a curve is usually an equation of a line, so Excel to calculate the coefficients and variables needed to calculate this line. It is obvious that this is not simple, you need the formulas to calculate the coordinates of the point of tangency is a point on the line, must be points of intersections with X and Y. This will make three points is already one too many for a right.

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