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Trigonometry — Revision Notes

Tamil Nadu Board · Class 9 · Mathematics

Trigonometry revision notes for Tamil Nadu Board Class 9 Mathematics: 4 topics in quick points. Part of the Tamil Nadu Board Class 9 Mathematics syllabus.

45 questions30 flashcards4 formulas & key relations5 concepts

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A labeled diagram of a right-angled triangle showing the perpendicular, base, and hypotenuse relative to an acute angle, and defining the six trigonometric ratios (sine, cosine, tangent, cosecant, sec
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Key Topics to Revise

1

1. Introduction to Trigonometric Ratios

  • Trigonometry deals with relationships between sides and angles of right-angled triangles
  • Three sides of a right-angled triangle: opposite (to the given angle), adjacent (to the given angle), and hypotenuse (longest side)
  • Trigonometric ratios are unitless numbers (pure ratios of lengths)
2

2. Reciprocal Trigonometric Ratios

  • Three reciprocal ratios exist: cosecant, secant, and cotangent
  • Each reciprocal ratio inverts one of the basic ratios
  • Reciprocal ratios are useful in simplifying trigonometric expressions
3

3. Trigonometric Ratios of Special Angles (0°, 30°, 45°, 60°, 90°)

  • Special angles have exact trigonometric values that must be memorized
  • 45° comes from isosceles right triangles (sides in ratio 1:1:√2)
  • 30° and 60° come from equilateral triangles (sides in ratio 1:√3:2)
4

4. Trigonometric Ratios of Complementary Angles

  • Two angles are complementary if their sum equals 90°
  • In a right triangle, the two acute angles are always complementary
  • sin θ = cos(90° - θ) for any acute angle θ

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Full Notes

Key Concepts

In a rightThe reciprocals of the basic trigonometricCertain angles have wellTwo angles are complementary if theirTrigonometric tables provide pre

Frequently Asked Questions

What are the important topics in Trigonometry for Tamil Nadu Board Class 9 Mathematics?
Key topics in Trigonometry include Introduction to Trigonometric Ratios, Reciprocal Trigonometric Ratios, Trigonometric Ratios of Special Angles (0°, 30°, 45°, 60°, 90°), Trigonometric Ratios of Complementary Angles. Study these first, then practise questions on each for Class 9 exams.
How should I revise Trigonometry for Class 9 exams?
Learn the core ideas first, then work through the 45 practice questions on Trigonometry. 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.

More resources for Trigonometry

All Tamil Nadu Board Class 9 Mathematics Revision Notes

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