Relations Between Sides and Angles of a Triangle — Concept Maps
NIOS · Class 12 · Mathematics
3 concept maps of Relations Between Sides and Angles of a Triangle for NIOS Class 12 Mathematics, each also written out as a text outline.
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Chapter Overview: Relations Between Sides and Angles of a Triangle
The map in words
- root((Triangle
- Formulas))
- Notation
- BC = a opposite A
- CA = b opposite B
- AB = c opposite C
- A plus B plus C = 180 deg
- Sine Formula
- a over sinA = b over sinB = c over sinC
- Set equal to k
- a = k sinA
- b = k sinB
- c = k sinC
- Proof Uses Altitude
- Three Cases
- Cosine Formula
- cosA = b sq + c sq minus a sq over 2bc
- cosB = c sq + a sq minus b sq over 2ac
- cosC = a sq + b sq minus c sq over 2ab
- SSS Case
- SAS Case
- Special When A = 60 deg
- b sq + c sq minus a sq = bc
- Projection Formula
- a = b cosC + c cosB
- b = c cosA + a cosC
- c = a cosB + b cosA
- Geometric Meaning
- Projection of Sides
- Key Identities
- sin sq A minus sin sq B
- = sinA+B times sinA-B
- B+C over 2 = 90 minus A over 2
- sinB+C over 2 = cos A over 2
- cosB+C over 2 = sin A over 2
- sin sq A minus sin sq B
- Notation
Relations Between Sides and Angles - Complete Overview
The map in words
- Triangle Relations
- Sine Formula
- Application: AAS, ASA cases
- Form: a/sin A = b/sin B = c/sin C
- Use: Find unknown sides from angles
- Use: Find unknown angles from sides
- Cosine Formula
- Application: SSS, SAS cases
- Form: cos A = (b² + c² - a²)/(2bc)
- Check: Right angle detection
- Use: Pythagorean generalization
- Projection Formula
- Application: Express sides
- Form: a = b cos C + c cos B
- Geometric: Projection interpretation
- Derive: Foundation for Sine Formula
- Triangle Elements
- Sides: a, b, c
- Angles: A, B, C
- Constraint: A + B + C = π
- Convention: Side opposite angle
- Sine Formula
Decision tree for choosing the right formula based on known information
The map in words
- Know two angles and one side?
- Yes: Use Sine Formula
- Calculate missing side or angle
- No: Know two sides and angle?
- Between sides: Use Cosine Formula
- Opposite to one side: Use Sine Formula
- Yes: Use Sine Formula
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