Class 9 Maths Chapter 5 Exercise 5.2 Solutions – Central Angles and Chords

Class 9 Maths Chapter 5 Exercise 5.2 Solutions (Ganita Manjari 2026) – Central Angles and Chords

📘 NCERT Ganita Manjari (2026) 📚 CBSE 2026–27 🏆 Step-by-Step Solutions

Class 9 Maths Exercise 5.2 Solutions

Central Angles and Chords – Step-by-Step NCERT Solutions

Prepare with complete Class 9 Maths Chapter 5 Exercise 5.2 Solutions based on the latest NCERT Ganita Manjari (2026). This exercise focuses on the angle subtended by a chord at the centre of a circle, the relationship between equal chords and equal central angles, and the theorems connecting these two ideas. Learn each theorem through step-by-step proofs using triangle congruence before solving the exercise questions.

📖
Exercise
5.2
Questions
2 Questions
📚
Coverage
Central Angles &
Chords
🧠
Skills
Theorems &
Proofs
⏱️
Study Time
25–35 Min
Difficulty
Moderate
🎯
Exam Importance
★★★★★
🎯 By the End of This Exercise, You Will Be Able To…
✅ Identify the Central Angle Subtended by a Chord
✅ Understand the Relationship Between Equal Chords and Central Angles
✅ Prove the Equal Chords Theorem Using SSS Congruence
✅ Prove the Converse Using SAS Congruence
✅ Apply These Theorems to Chord-Based Problems
✅ Write Clear Step-by-Step Geometry Proofs

📑 Table of Contents

📖 About Class 9 Maths Chapter 5 Exercise 5.2

Class 9 Maths Chapter 5 Exercise 5.2 is the second exercise of Chapter 5 – I’m Up and Down, and Round and Round from the latest NCERT Ganita Manjari (2026). This exercise focuses on the relationship between chords and the angles they subtend at the centre of a circle, with questions based on the theorems introduced in this part of the chapter.

This page provides the complete Exercise Set 5.2 in a clear, step-by-step format, including the relevant theorem proofs and question-wise solutions. The presentation follows a student-friendly CBSE answer-writing approach and is designed for classroom practice, homework, self-study and revision.

🎯 Exercise Snapshot

📘 What You’ll Find
  • Complete Exercise Set 5.2 coverage.
  • NCERT-based solutions for both exercise questions.
  • Relevant theorem statements and step-by-step proofs.
📚 Page Includes
  • Central-angle and chord-based explanations.
  • Theorem proofs presented step by step.
  • Question-wise solutions with clear reasoning.
🏆 Best For
  • Students studying the new Ganita Manjari textbook.
  • Homework and classroom practice.
  • Revision and CBSE examination preparation.
📚 Learn Before We Solve
Build the concept first, then solve Exercise 5.2.
📐 Central Angle and Chord
A chord joined to the centre forms a central angle.
🎯 What is a Central Angle?
Take a chord AB of a circle and join its endpoints A and B to the centre O.
The angle formed at the centre is called the angle subtended by the chord at the centre.
Here, AB is the chord and ∠AOB is the central angle.
Central angle subtended by chord AB at centre O, showing radii OA and OB and angle AOB
💡 Key Observation
OA and OB are radii of the same circle. Therefore,
OA = OB
So, △AOB has two equal sides. Therefore, it is an isosceles triangle.
🧠 Remember
Chord + Centre → Two radii → Equal sides → Isosceles triangle
Theorem 2
Equal Chords Subtend Equal Angles at the Centre
Equal chords of a circle subtend equal angles at the centre of the circle.
Given:
AB = DE
To show:
∠ACB = ∠DCE
📐 Figure
Equal chords AB and DE of a circle with centre C, showing triangles ACB and DCE
✍️ Proof
Consider the two triangles △ACB and △DCE.

Since CA, CB, CD and CE are radii of the same circle,
CA = CD
and
CB = CE
Also, it is given that
AB = DE
Therefore,
△ACB ≅ △DCE
by SSS congruence.
Therefore, corresponding angles of congruent triangles are equal by CPCT.
∠ACB = ∠DCE
✅ Hence Proved
∠ACB = ∠DCE
🧠 Remember
Equal chords → SSS congruence → Equal angles by CPCT
Theorem 3
Equal Central Angles Give Equal Chords
Chords of a circle that subtend equal angles at the centre are equal.
Given:
∠ACB = ∠DCE
To show:
AB = DE
📐 Figure
Circle with centre C, chords AB and DE, and equal central angles ACB and DCE
✍️ Proof
Consider the two triangles △ACB and △DCE.

Since CA, CB, CD and CE are radii of the same circle,
CA = CD
and
CB = CE
Also, it is given that
∠ACB = ∠DCE
Therefore,
△ACB ≅ △DCE
by SAS congruence.
Therefore, corresponding sides of congruent triangles are equal by CPCT.
AB = DE
✅ Hence Proved
AB = DE
🧠 Remember
Equal central angles → SAS congruence → Equal chords by CPCT
💡 Solved Model Problem
See how the radius property helps us recognise an isosceles triangle.
Model Question
A chord AB of a circle with centre O is joined to the centre. Show that the triangle formed is an isosceles triangle.
Given:
AB is a chord of a circle with centre O.
To show:
△OAB is an isosceles triangle.
📐 Figure
Class 9 Maths Chapter 5 Exercise 5.2 diagram showing chord AB joined to centre O, forming isosceles triangle OAB
✍️ Solution
Join the endpoints A and B of the chord to the centre O.

Now, OA and OB are radii of the same circle. Therefore,
OA = OB
Thus, two sides of △OAB are equal.
A triangle having two equal sides is called an isosceles triangle.
✅ What We Learned
The two sides from the centre to the endpoints of a chord are radii, so they are always equal.
🧠 Now Connect It to Exercise 5.2
If two chord-centre triangles are compared, their corresponding radii are equal automatically.
So, when the question gives us an equal chord or an equal central angle, we can use SSS or SAS congruence to prove the required result.

📝 Class 9 Maths Chapter 5 Exercise 5.2 Solutions

Solve every question of Class 9 Maths Chapter 5 Exercise 5.2 with clear, step-by-step NCERT Ganita Manjari (2026) solutions. This exercise focuses on important ideas involving central angles, chords, equal chords, and the related theorems. The theorem proofs and question-wise solutions are presented in a simple, student-friendly CBSE answer-writing style with clear reasoning, making this page useful for classroom work, homework, revision, and examination preparation.

📝 Step-by-Step Solutions 🎯 NCERT & CBSE Aligned ⭐ Complete Exercise 5.2
Question 1
Show that the triangle formed by a chord and the centre of the circle is isosceles.
✍️ Solution
Given,
AB is a chord of a circle with centre O.
To prove,
△OAB is an isosceles triangle.

📐 Figure

Chord AB joined to the centre O A circle with centre O and chord AB. The endpoints A and B are joined to O, forming triangle OAB. A B O OA OB Chord AB

Figure: Chord AB is joined to the centre O.

✍️ Proof

Consider △OAB.

Since OA and OB are radii of the same circle,
OA = OB
Thus, two sides of △OAB are equal.

Therefore, △OAB is an isosceles triangle.
✅ Hence Proved
△OAB is an isosceles triangle.
🧠 Remember
Two radii of the same circle are equal. Therefore, the triangle formed by a chord and the centre is isosceles.
Question 2
Show that if two such isosceles triangles (occurring in the previous question) have equal base length, they are congruent to each other.
✍️ Solution
Given:
AB and DE are two equal chords of the same circle.
AB = DE
To prove:
△ACB ≅ △DCE

📐 Figure

Two isosceles triangles ACB and DCE with equal bases AB and DE in the same circle

Figure: Two isosceles triangles ACB and DCE in the same circle with equal bases AB and DE.

✍️ Proof

Consider the two triangles
△ACB and △DCE
Since CA, CB, CD and CE are radii of the same circle,
CA = CD
and
CB = CE
Also, it is given that the two bases are equal:
AB = DE
Therefore, the three corresponding sides of the two triangles are equal:
CA = CD
CB = CE
AB = DE
Hence,
△ACB ≅ △DCE
by SSS congruence.
✅ Hence Proved
△ACB ≅ △DCE
🧠 Remember
Same circle → all radii are equal.
Equal bases + equal radii → SSS → congruent triangles.

📚 Continue Learning

Congratulations! You have completed Class 9 Maths Chapter 5 Exercise 5.2 Solutions. You have now worked through the second exercise of Chapter 5 – I’m Up and Down, and Round and Round, including central angles, chords and the related theorems. Continue your learning journey by revisiting Exercise 5.1, exploring the complete chapter, or moving to the next exercise when it becomes available.


📖 Explore More Class 9 Maths Chapters

❓ Frequently Asked Questions

Find answers to common student questions about Class 9 Maths Exercise 5.2. These FAQs clarify the central-angle concept, the relationship between chords and angles at the centre, and the theorem-based reasoning used in the exercise.

What is the main focus of Exercise Set 5.2?

Exercise Set 5.2 focuses on the angle subtended by a chord at the centre of a circle and the relationship between chords and these central angles. The exercise also uses the properties of the triangles formed by joining the centre to the endpoints of a chord.

What is a central angle in this exercise?

When the endpoints of a chord are joined to the centre of the circle, the angle formed at the centre is the angle subtended by that chord at the centre. For a chord AB and centre O, this angle is written as ∠AOB.

What is the theorem about equal chords and central angles?

The theorem states that equal chords of a circle subtend equal angles at the centre of the circle. In the proof, the radii and equal chords provide three pairs of equal sides, so the two triangles are proved congruent by SSS. Corresponding angles are then equal.

What is the converse theorem used in Exercise 5.2?

The converse states that chords of a circle that subtend equal angles at the centre are equal. Its proof uses the equal radii together with the equal central angles to establish triangle congruence by SAS. Corresponding chords are then equal.

Why does joining a chord to the centre form an isosceles triangle?

If a chord AB is joined to the centre O, the segments OA and OB are radii of the same circle. Therefore, OA = OB. Since two sides of triangle OAB are equal, the triangle is isosceles.

Why is SSS congruence used in the equal-chords theorem?

For two equal chords, the corresponding segments from the centre are radii and are therefore equal. Together with the equal chords, this gives three pairs of equal corresponding sides. Hence, the triangles can be proved congruent by SSS.

Why is SAS congruence used in the converse theorem?

In the converse theorem, the corresponding radii are equal because they belong to the same circle, and the included central angles are given equal. Thus, two corresponding sides and the included angle are equal, so SAS congruence proves that the triangles are congruent.

Are these Class 9 Maths Exercise 5.2 Solutions based on Ganita Manjari 2026?

Yes. This page follows Chapter 5 – I’m Up and Down, and Round and Round from the NCERT Ganita Manjari (2026) textbook and covers the material and questions of Exercise Set 5.2. The page presents the relevant theorem proofs and the two exercise questions in a step-by-step, student-friendly format.

📚 Useful Learning Resources

Continue your preparation with more Class 9 Maths resources from Maths Gurukulam, or visit the official NCERT and CBSE websites for the latest textbooks, syllabus, and academic updates.

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Teaching CBSE Mathematics Since 2006

These Class 9 Maths Chapter 5 Exercise 5.2 Solutions are carefully prepared according to the latest NCERT Ganita Manjari (2026) and the CBSE curriculum. The solutions follow a clear, step-by-step approach to help students understand the central-angle and chord relationships, theorem-based reasoning, and problem-solving methods used in Exercise 5.2.

📘 NCERT Ganita Manjari (2026) 🎯 CBSE Aligned 📝 Step-by-Step Solutions 💡 Concept-Based Learning
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