How to draw tangent line in a curve?

I want to draw tangent line in a curve. I know that the line must cross axes's origin, how i can do it?? I have thought to calculate derivative with command diff(y) and define the passage from point (0,0), but i don't know to do this. Thanks

This is the curve

[Robert]

There is one tangent line that happens to cross the origin but it isn't tangent at the red dot in your figure. In general, tangent lines do not need to cross the origin.

Do you need it to cross the origin, or to be tangent at the red point?

[Gregorio Stiuso]

Yes, i need to have a tangent line that cross the origin.

[Thorsten]

That's not a tangent. Please see my updated answer below of how to do it.

Answer 1

[Thorsten]

You can compute the slope with diff. Next you have to compute the y-values for x = 0 and x = 1 and plot the line. This link gives the formula:

https://de.mathworks.com/matlabcentral/answers/87543-how-to-draw-tangent-line-at-specified-points-in-a-curve

If you want to draw a line from 0,0 through x1, x2 to the right y-axis, use

 line([0 max(xlim)], [0, y1/x1*max(xlim)])