Definition of a Circle
A circle is the set of all points in a plane that are at the same distance from a fixed point called the centre. This fixed distance is called the radius.
Practice This ConceptMain explanation
Teacher explanation
Think of the centre as the fixed point and the radius as the equal distance rule. Every point on the boundary follows this rule. A diameter is a chord passing through the centre and its length is twice the radius.
Example
If O is the centre and radius is 5 cm, then every point P on the circle has OP = 5 cm. A diameter of this circle is 10 cm.
Simple analogy
Same distance from centre means circle.
Common confusion
Students often call the full circular region a circle. In school geometry, the circle usually means the boundary, while the region inside is the circular region or disc.
Exam tip
When a radius is drawn to a point on the circle, immediately mark it equal to every other radius from the same centre.
Answer writing and exam use
1-mark use
Write the exact meaning of definition of a circle in one clean line.
2-mark use
Define definition of a circle and add one example or condition.
3-mark use
Explain definition of a circle, show the method or example, and mention the common mistake.
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