Recurrence Relations A recurrence relation defines a sequence in terms of its previous terms. Such relations occur frequently in mathematics, computer science, and discrete structures. Step Rule 1 Write the characteristic equation for the given recurrence relation. 2 Solve the characteristic equation and find all roots. 3 The order of the recurrence = highest index − lowest index. Nature of Roots Complementary Solution a n (h) Real and distinct λ₁ ≠ λ₂ ≠ … ≠ λₖ a n = C₁λ₁ n + C₂λ₂ n + … + Cₖλₖ n Real and equal λ₁ = λ₂ = … = λₖ a n = (C₁ + C₂n + C₃n² + …) λ₁ n Complex conjugate roots λ = α ± iβ a n = r n [ C₁ cos(nθ) + C₂ sin(nθ) ] where r = √(α² + β²), θ = tan −1 (β/α) f(n) Assumed Particular Solution a n (p) Constant (C) P₀ Polynomial a + bn + cn² + … P₀ + P₁n + P₂n² + … a·b n , b ≠ λ P₀·b n a·b n , b = λ (with multiplicity m) P₀·n m b n Total ...