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Tamil Nadu (TNBSE)Class 6 Mathematics★ 5-9 marks in the TN Class 6 Term 1 exam through angle classification and measurement

Geometry (Term 1) - Lines and Angles

Samacheer Kalvi (TN State Board) Class 6 Maths — Term 1 Chapter 4, Geometry. Points, lines, rays and line segments, measuring angles with a protractor, the types of angles, special angles (30°, 45°, 60°, 90°, 120°) and supplementary angles, with worked examples, exercises and quick revision.

⏱ 14 min readEasy difficulty✓ Free · NCERT-aligned

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Key points, glossary and the questions most likely to show up.

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By the end of this chapter you'll be able to…

1Distinguish points, lines, rays and segments
2Measure angles with a protractor
3Classify angles by their measure
4Construct special angles
5Find supplementary angles

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Why this chapter matters

Points, lines and angles are the building blocks of geometry. Classifying and measuring angles is directly tested in the TN Class 6 Term 1 exam and is needed for all later geometry.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

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Class 5 — Shapes and Angles

Basic shapes.

Geometry (Lines and Angles) — Class 6 Maths (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 6 Mathematics, Term 1 — Chapter 4. The basics of lines and angles.

1. About this chapter

This chapter covers points, lines, rays and line segments, measuring angles, the types of angles, special angles, and supplementary angles.

2. Basic terms

A point marks an exact position; a line extends endlessly in both directions; a ray starts at one point and goes on in one direction; a line segment has two endpoints.
An angle is formed when two rays meet at a common point (the vertex); it is measured in degrees (°) with a protractor.

3. Types of angles

Type	Measure
Acute	between 0° and 90°
Right	exactly 90°
Obtuse	between 90° and 180°
Straight	exactly 180°
Reflex	between 180° and 360°

Special angles often constructed: 30°, 45°, 60°, 90°, 120°.

4. Supplementary angles

Two angles are supplementary if they add up to 180°.
Example: the supplement of 110° is 180° − 110° = 70°.

5. Worked examples

Example 1. What type of angle is 75°? Acute (between 0° and 90°).

Example 2. Find the supplement of 130°. 180° − 130° = 50°.

Example 3. How many endpoints does a line segment have? Two.

6. Exercises (Samacheer Kalvi)

Name the figure with (a) no endpoints (b) one endpoint (c) two endpoints.
Classify: 40°, 90°, 135°, 180°.
Measure and draw an angle of 60° using a protractor.
Find the supplement of (a) 95° (b) 45°.
Draw a ray and mark a point on it.

7. Common mistakes

Mistake: Confusing a line, a ray and a segment. Fix: A line has no endpoints, a ray one, a segment two.
Mistake: Reading the protractor from the wrong scale. Fix: Start from 0° on the side aligned with one ray.
Mistake: Mixing up complementary (90°) and supplementary (180°). Fix: Supplementary angles add to 180°.

8. Quick revision

Term 1 · Ch 4 · lines and angles.
Point, line (no ends), ray (one end), segment (two ends); angle = two rays at a vertex, measured in degrees.
Acute < 90° < obtuse < 180° (straight) < reflex; special angles 30°, 45°, 60°, 90°, 120°.
Supplementary angles add to 180°.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Basic figures

line (no ends), ray (one end), segment (two ends)

By endpoints.

Angle

two rays meeting at a vertex; measured in degrees

Use a protractor.

Types

acute < 90° < obtuse < 180° (straight) < reflex

By measure.

Supplementary

two angles add to 180°

Supplement = 180° − angle.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Confusing a line, a ray and a segment

✓ A line has no endpoints, a ray one, a segment two.

WATCH OUT

✗ Reading the protractor from the wrong scale

✓ Start from 0° on the side aligned with one ray.

WATCH OUT

✗ Mixing up complementary (90°) and supplementary (180°)

✓ Supplementary angles add to 180°.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Basic figures

Name lines, rays and segments.

Questions

Classifying angles

Classify and measure angles.

Questions

Supplementary angles

Find supplements; construct special angles.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Classify

What type of angle is 75°?

▶ Show solution

Acute (between 0° and 90°).

Q2EASY· Supplement

Find the supplement of 130°.

▶ Show solution

50°.

Q3EASY· Figures

How many endpoints does a line segment have?

▶ Show solution

Two.

Q4EASY· Classify

Classify each: 40°, 90°, 135°, 180°.

▶ Show solution

Acute, right, obtuse, straight.

Q5EASY· Supplement

Find the supplement of 95°.

▶ Show solution

85°.

Q6MEDIUM· Construction

How do you draw a 60° angle with a protractor?

▶ Show solution

Draw a ray, place the protractor centre on its endpoint, mark 60° on the correct scale and join the point to the endpoint.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Term 1 Chapter 4 of Samacheer Kalvi Class 6 Maths.
•A line has no endpoints, a ray one, a segment two.
•An angle is formed by two rays at a vertex and is measured in degrees with a protractor.
•Acute < 90°, right = 90°, obtuse < 180°, straight = 180°, reflex < 360°.
•Special angles: 30°, 45°, 60°, 90°, 120°.
•Supplementary angles add up to 180°.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 5-9 marks across angles and figures

Question type	Marks each	Typical count	What it tests
Objective	1	3-4	Figures and angle types
Supplement	1	1-2	Finding supplements
Construction	2	1	Drawing/measuring angles

Prep strategy

Learn the endpoint rule for figures
Practise reading the protractor scale
Memorise the angle-type ranges
Use 180° for supplements

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Drawing and design

Angles are used in art, maps and plans.

Construction

Builders set accurate angles for corners.

Navigation

Directions are measured as angles.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

State the endpoint rule for figures
Read the protractor from the correct 0°
Match each angle to its type
Subtract from 180° for supplements

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Two supplementary angles are in the ratio 2 : 3. Find them.
Construct a 105° angle using a protractor and check with a ruler.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 6 Term 1 ExamHigh

NMMS / Foundation MathsMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

A ray starts at one endpoint and extends endlessly in one direction, while a line segment has two endpoints and a definite length.

Place the centre of the protractor on the angle's vertex with the baseline along one ray, then read the scale that starts from 0° on that ray.

Practice more, ask doubts, find a tutor

Tamil Nadu (TNBSE) Class 6 mock tests

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