Two-dimensional figure consisting of the set of all the points that are equally distant from the same point called the centre of the circle.
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In this figure :
- the point O is the centre of the circle,
- \(\overline{\textrm{OE}}\) is a radius of the circle,
- \(\overline{\textrm{AD}}\) is a diameter of the circle,
- \(\overline{\textrm{FG}}\) is a chord of the circle,
- \(\overline{\textrm{TD}}\) is tangent to the circle at point D.
Notation
Common notations for the circle are d for the diameter, r for the radius and C for the circumference. The letter O refers to the centre of the circle.
Formulas
The formulas used to calculate the circumference C and the area A of a circle are the following :
- \(C = 2π r\)
- \(A = πr^2\) or \(A = \dfrac{πd^2}{4}\)