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# Plot x^2+y^2=4

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Mohamed Lawindy on 25 Feb 2020
Commented: Mohamed Lawindy on 25 Feb 2020
Hello, I have a little starter question about matlab. How do I plot a circle given by x^2+y^2=4?
Thank you.
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### Accepted Answer

Sky Sartorius on 25 Feb 2020
There are a few ways to go about this. One that is somewhat agnostic to what the equation is trying to represent (in this case, a circle) involves calculating the equation for the whole space, then plotting only an isoline of the target value.
[X,Y] = meshgrid(-3:.1:3,-3:.1:3); % Generate domain.
Z = X.^2 + Y.^2; % Find function value everywhere in the domain.
contour(X,Y,Z,[4 4]) % Plot the isoline where the function value is 4.
If you know more about your function and can turn it around into a function of only one variable (e.g., sine and cosine of t), that is preferable in most cases.
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Mohamed Lawindy on 25 Feb 2020
Thank you very much.

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### More Answers (1)

James Tursa on 25 Feb 2020
E.g., since you know it is a circle with radius 2 centered at the origin;
ang = 0:0.01:2*pi;
x = 2*cos(ang);
y = 2*sin(ang);
plot(x,y);
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Mohamed Lawindy on 25 Feb 2020
Thank you too.

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