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Circles Final Part | Class 9 Math | Chapter Revision & Important Questions | MD Sir
Revise the entire Class 9 Math chapter on Circles with key concepts, important formulas, and solved examples. Learn how to tackle questions on tangents, chords, and circles to ace your board exams.
Points to be Covered:
Introduction to Circles
Definition of a circle, center, radius, and diameter
Parts of a circle: Chord, tangent, secant, arc, and sector
Real-life examples of circles
Basic Terminology and Definitions
Radius, diameter, and circumference
Chord and its properties
Secant and tangent to a circle
Relationship between radius, diameter, and circumference
Important Theorems on Circles
Theorem 1: The perpendicular from the center of a circle to a chord bisects the chord
Theorem 2: The line joining the center of the circle to the midpoint of the chord is perpendicular to the chord
Theorem 3: Equal chords of a circle are equidistant from the center
Theorem 4: The lengths of two tangents drawn from an external point to a circle are equal
Tangents to a Circle
Definition of a tangent to a circle
Properties of tangents: A tangent is perpendicular to the radius at the point of contact
Example problems on finding the length of the tangent from a point outside the circle
The concept of two tangents drawn from the same external point
Chords and Arcs
Definition of a chord and an arc
Relationship between chords, their distances from the center, and the angles subtended by them
Problems involving the measurement of chords and arcs
Angle Subtended by a Chord at the Center
Theorem: The angle subtended by a chord at the center is twice the angle subtended at any point on the remaining part of the circle
Solving problems related to angles formed by chords and their properties
Important Formulas to Remember
Circumference of a circle: C=2πrC = 2\pi rC=2πr
Area of a circle: A=πr2A = \pi r^2A=πr2
Length of an arc: L=θ360×2πrL = \frac{\theta}{360} \times 2\pi rL=360θ×2πr
Area of a sector: A=θ360×πr2A = \frac{\theta}{360} \times \pi r^2A=360θ×πr2
Practice Problems
Solving a variety of problems involving tangents, chords, and angles in circles
Step-by-step explanation of problems from NCERT and previous years
Application of theorems and formulas in different question types
Key Takeaways for Exam Preparation
Master the key theorems and their applications in different scenarios
Focus on understanding the relationship between the radius, chord, tangent, and angles
Practice diagram-based problems to visualize and solve efficiently
Final Revision Tips
Revise the main properties and theorems carefully
Practice with real exam questions to improve problem-solving skills
Manage time effectively during the exam, especially in diagram-based questions
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