![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/250989/image.png)
How to draw the tangent to a curve passing through the origin
13 views (last 30 days)
Show older comments
Hi,
I have the following code
xt = -1:0.1:1;
yt=-100-(2*(cos(xt)).^3)-(4*(cos(xt)).^2)-3*cos(xt);
plot(xt,yt)
and I get the blue curve as below. Now, I want to add a tangent line which must pass through the origin (as the black line I added "by hand" in the figure below).
I was thinking to use the function gradient but I am not sure how to impose the condition to pass through the (0,0).
Could you help me?
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/250924/image.jpeg)
0 Comments
Accepted Answer
Akira Agata
on 28 Nov 2019
Edited: Akira Agata
on 28 Nov 2019
Assuming that you want to obtain tangent lines which pass through the (-110,0), how about the following?
In this code, I changed delta xt from 0.1 to 0.01 in order to obtaion more accurate result.
xt = -1:0.01:1;
yt =-100-(2*(cos(xt)).^3)-(4*(cos(xt)).^2)-3*cos(xt);
dyt = gradient(yt,0.01);
% yt value of tangent line at xt = 0 for each point on the curve
ytValue = yt - xt.*dyt;
% Find the xt positions where ytValue is close to -110
[~,pt] = mink(abs(ytValue + 110),2);
% Tangent line
ytTangent1 = dyt(pt(1))*(xt - xt(pt(1))) + yt(pt(1));
ytTangent2 = dyt(pt(2))*(xt - xt(pt(2))) + yt(pt(2));
% Draw the curve and the tangent line
figure
plot(xt,yt)
hold on
plot(xt,ytTangent1)
plot(xt,ytTangent2)
grid on
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/250989/image.png)
0 Comments
More Answers (0)
See Also
Categories
Find more on Interpolation in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!