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Revision Notes

Complementary Angles

ICSE · Class 9 · Mathematics

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

44 questions22 flashcards5 concepts

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An illustration showing two acute angles whose sum is 90 degrees, defining them as complementary angles. Examples like 30 and 60 degrees, and a general case with x and (90-x) degrees.
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Key Topics to Revise

1

Basic Concept of Complementary Angles

  • Two acute angles are complementary if their sum is 90°
  • Examples: 30° and 60°, 45° and 45°, 70° and 20°
  • If one angle is θ, its complement is (90° - θ)
2

Sine and Cosine Relationships

  • sin(90° - θ) = cos θ
  • cos(90° - θ) = sin θ
  • These relationships are reciprocal - sine of an angle equals cosine of its complement
3

Tangent and Cotangent Relationships

  • tan(90° - θ) = cot θ
  • cot(90° - θ) = tan θ
  • Tangent and cotangent are also co-functions
4

Secant and Cosecant Relationships

  • sec(90° - θ) = cosec θ
  • cosec(90° - θ) = sec θ
  • These are reciprocal function relationships

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Full Notes

Key Concepts

Two acute angles are complementary ifFor complementary anglesFor complementary anglesFor complementary anglesIn a right triangle ABC

Frequently Asked Questions

What are the important topics in Complementary Angles for ICSE Class 9 Mathematics?
Complementary Angles 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 Complementary Angles — ICSE Class 9 Mathematics?
Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision 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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