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## JSS1: MATHEMATICS - 2ND TERM

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Lesson 6, Topic 4
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# Circles – Properties of Plane Shapes

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A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point. The centre: equivalently, it is the curve traced out by a point that moves in a plane.

Area of a circle = $$\scriptsize \pi r^2$$

Area of a semi circle = $$\frac {1}{2} \scriptsize \pi r^2$$

• The circumference is the distance around the circle.
• A radius (Plural radii) is any straight line joining the centre of the circle to any point on the circumference.
• A diameter is a straight line joining two points on the circumference and passes through the centre of the circle. The diameter divides a circle into two equal parts. Each part is called a semicircle.
• An arc is a part of the circumference of a circle.
• A chord is a straight line joining two points on the circumference.
• A segment is a region between a chord and the circumference.
• A sector is a region between two radii and the circumference.