find values for the equation of a circle
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I have the equation of a circle:
(x - a)^2 + (y - b)^2 - r^2 = 0
a, b and r are known values but I would like to find the values of x and y from a predetermined coordinate matrix which satisfies the equation.
example: a = 2, b = 2, r = 2
A =
1 2
1 3
2 4
hence the last row in A(2,4) would satisfy the equation. i.e. x = 2, y = 4
this is what I've tried so far:
a = 2;
b = 2;
r = 2;
x = find(A(:,1);
y = find(A(:,2);
solve((x - a)^2 + (y - b)^2 - r^2 == 0)
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Réponse acceptée
Roger Stafford
le 14 Août 2014
Modifié(e) : Roger Stafford
le 14 Août 2014
a = 2; b = 2; r = 2;
A = [1 2;1 3;2 4];
B = A((A(:,1)-a).^2+(A(:,2)-b).^2==r^2,:);
B contains the coordinate pairs, if any, that lie on the circle. Note that if you need this for values of a, b, and c which are not integers, it is best to allow a small tolerance for round-off errors rather than demanding exact equality in the equation.
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