http://mathworld.wolfram.com/Circle-CircleIntersection.html
A is your first point.
B is the point that should circle it.
C is the point you move A to.
D is the point to which B should move to.
R is the distance between point A and B.
E is a circle centered at point A, with radius R.
F is a circle centered at point C, with radius R.
Find the point(s) where circles E and F intersect.
If the circles intersect at one point, that point is point D.
If the circles intersect at two points, determine the squared distance of each from point B. Choose the one with the smaller squared distance. That is point D.
If the circles intersect at an imaginary point, subtract point A from point C to create a vector, calculate the length of the vector, divide the vector by it's length, and then multiply by R. That is point D.
I think.
A is your first point.
B is the point that should circle it.
C is the point you move A to.
D is the point to which B should move to.
R is the distance between point A and B.
E is a circle centered at point A, with radius R.
F is a circle centered at point C, with radius R.
Find the point(s) where circles E and F intersect.
If the circles intersect at one point, that point is point D.
If the circles intersect at two points, determine the squared distance of each from point B. Choose the one with the smaller squared distance. That is point D.
If the circles intersect at an imaginary point, subtract point A from point C to create a vector, calculate the length of the vector, divide the vector by it's length, and then multiply by R. That is point D.
I think.