I'm Up and Down, and Round and Round
CBSE · Class 9 · Mathematics
Summary of I'm Up and Down, and Round and Round for CBSE Class 9 Mathematics. Key concepts, important points, and chapter overview.
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Overview
A circle is the set of all points on a plane that are at the same distance from one fixed point called the centre. The chapter builds the full geometry of circles from this basic idea. It explains radius, chord, diameter, arc, circumcircle, circumcentre, cyclic quadrilateral, and the major theorems
Key Concepts
A circle is the set
A circle is the set of all points equidistant from a fixed point. That fixed point is the centre, and the common distance from the centre to any point
A chord is a line segment
A chord is a line segment joining two points on a circle. A diameter is a chord passing through the centre. The diameter is the greatest chord.
An arc is a connected portion
An arc is a connected portion of a circle between two end points. If the central angle is less than 180°, the arc is minor; if it is greater than 180°
A circle has complete rotational symmetry
A circle has complete rotational symmetry: rotating it about its centre by any angle leaves it unchanged. Every diameter is a line of reflection symme
There is exactly one circle passing
There is exactly one circle passing through three non-collinear points. Its centre is the circumcentre, found at the intersection of the perpendicular
Learning Objectives
- Understand the definition of a circle, its centre, radius, chord, diameter, and arc
- Recognise rotational symmetry and reflection symmetry in a circle
- Find the unique circle through three non-collinear points and locate the circumcentre
- Use congruence to prove results about equal chords and equal angles at the centre
- Apply perpendicular bisector properties of chords
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Sources & Official References
- NCERT Official — ncert.nic.in
- CBSE Academic — cbseacademic.nic.in
- CBSE Official — cbse.gov.in
- National Education Policy 2020 — education.gov.in
Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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