# How do you express how much a curve or part of a circle is “bent”?

Given a certain curve, or part of a circle, how do you express how much it is bent?

If I have for example 1/3 of a circle (without seeing the full circle). How do I calculate and express that it is bent in a way that it forms 1/3 of a circle.

And as a follow-up on this question, how can I then construct the full circle, from this data.

Excuse me if it is unclear, it's hard for me to explain this in English.

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What information do you have available to you? If it is feasible for you to read off the first and second derivative of the curve you can see, then you can find the radius of the circle (See en.wikipedia.org/wiki/Curvature#Curvature_of_a_graph) which is then enough to draw the full circle. – Ragib Zaman Sep 26 '11 at 15:02
To repeat the comment of @Ragib Zaman, what does given mean here? There is the Euclidean geometry construction, pick two points on the given part. Find the perpendicular bisector. Do this again with two other points. The two perpendicular bisectors meet at the centre of the circle. – André Nicolas Sep 26 '11 at 15:16