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Key Concepts
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1. Direction Cosines (l, m, n)
If a vector makes angles α, β, γ with X, Y, Z axes respectively:
- l = cos α
- m = cos β
- n = cos γ
Identity: l² + m² + n² = 1
2. Direction Ratios (a, b, c)
Any three numbers proportional to direction cosines are called direction ratios. Relationship: l = a/√(a²+b²+c²).