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.
Key Topics to Revise
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)
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
Tangent and Cotangent Relationships
- tan(90° - θ) = cot θ
- cot(90° - θ) = tan θ
- Tangent and cotangent are also co-functions
Secant and Cosecant Relationships
- sec(90° - θ) = cosec θ
- cosec(90° - θ) = sec θ
- These are reciprocal function relationships
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