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Triangles

ICSE · Class 9 · Mathematics

Quick revision notes for Triangles — ICSE Class 9 Mathematics. Key concepts, formulas, and definitions for last-minute revision.

40 questions30 flashcards5 concepts

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A labeled diagram showing the vertices, sides, and angles of a basic triangle ABC.
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Key Topics to Revise

1

1. Basic Ideas and Side-Angle Relations

  • A triangle has three sides and three vertices.
  • Triangle ABC is used as the main example, with sides AB, BC and CA and vertices A, B and C.
  • If all sides of a triangle are different, then all angles are different.
2

2. Medians, Centroid, Altitudes and Orthocentre

  • The median of a triangle is the line joining the mid-point of a side with the opposite vertex.
  • A triangle has three medians.
  • The three medians are concurrent and meet at one point called the centroid.
3

3. Angle Sum, Exterior Angles and Corollaries

  • The sum of the angles of a triangle equals 180 degrees.
  • An exterior angle of a triangle equals the sum of the two interior opposite angles.
  • An exterior angle of a triangle is greater than each of the interior opposite angles.
4

4. Congruent Triangles and CPCTC

  • Two triangles are congruent if, on placing one over the other, they exactly coincide.
  • Congruent triangles have the same shape and the same size.
  • In congruent triangles, corresponding sides are equal and corresponding angles are equal.

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Full Notes

Key Concepts

A triangle is a plane figureThe greater side has the greaterThe median of a triangle correspondingThe centroid is the point whereAn altitude of a triangle corresponding

Frequently Asked Questions

What are the important topics in Triangles for ICSE Class 9 Mathematics?
Triangles covers several key topics that are frequently asked in ICSE Class 9 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Triangles — ICSE Class 9 Mathematics?
Understand the core concepts first, then work through the 40 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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