# Draw a tangent line with a given slope in Log scale

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Mohiedin Bagheri on 10 Sep 2021
Edited: Mohiedin Bagheri on 12 Sep 2021
Dear all,
I have a graph datapoints loaded in MATLAB. Y axis is Voltage (E) and x-axis is in Log scale. I have to draw a tangent line to this curve with a given of 50 V/dec in MATLAB. I also need to find the point where the tangent line crosses the curve. I appreciate that if someone could help.

Sulaymon Eshkabilov on 10 Sep 2021
To compute the tangent line of this curve, I would do the followings:
(1) Get the numerical data of the curve (shown in your plotted Figure)
(2) Find the polynomial (quadratic) fit model E(x) formulation using, e.g.: fit() or polyfit() or ...
(3) Take a symbolic derivative of E(x) formulation => dE(x)
(4) Compute dE(50) and E(50)
(5) Plug in the computed values in step 5 into this equation: y = dE(50)*(x-50) + E(50). This would be the tangent line equation for that point of x = 50.
(6) Plot the found tangent line data along with the original curve data.
Mohiedin Bagheri on 12 Sep 2021
@Sulaymon Eshkabilov attached is my .m file data. Thank you