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Revision Notes

Triangles — Revision Notes

ICSE · Class 9 · Mathematics

Triangles revision notes for ICSE Class 9 Mathematics: 4 topics in quick points. Part of the ICSE Class 9 Mathematics syllabus.

40 questions30 flashcards5 formulas & key relations5 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?
Key topics in Triangles include Basic Ideas and Side-Angle Relations, Medians, Centroid, Altitudes and Orthocentre, Angle Sum, Exterior Angles and Corollaries, Congruent Triangles and CPCTC. Study these first, then practise questions on each for Class 9 exams.
How should I revise Triangles for Class 9 exams?
Learn the core ideas first, then work through the 40 practice questions on Triangles. Revise 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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All ICSE Class 9 Mathematics Revision Notes

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