Bonsoir, Qui peut m’aider à faire l’exercice 4

Bonjour,

(Un) suite arithmétique de raison r et de 1er terme U₀

⇒ Un = U₀ + nr

⇒ U₀ = Un - nr

a) U₁ = 2 et r = -3

U₀ = U₁ - 1x(-3) = 2 + 3 = 5

U₁₆ = U₀ + 16r = 5 - 16x3 = -43

b) U₂ = 13 et r = -1,5

U₀ = U₂ - 2r = 13 + 3 = 15

U₁ = U₀ + r = 15 - 1,5 = 13,5

U₁₆ = U₀ + 16r = 15 - 16x1.5 = -9

c) U₃₁ = 17 et r = -3/2

U₀ = U₃₁ - 31r = 17 - 31x3/2 = 34/2 - 93/2 = -59/2

U₁ = U₀ + r = -59/2 - 3/2 = -62/2 = -31

U₁₆ = U₀ + 16r = -59/2 - 16x3/2 = -107/2

d) U₉ = 11/3 et r = 4/3

U₀ = U₉ - 9r = 11/3 - 36/3 = -25/3

U₁ = U₀ + r = -25/3 + 4/3 = -21/3 = -7

U₁₆ = U₀ + 16r = -25/3 + 64/3 = 39/3= 13