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Sagot :

Bonjour,

Formule explicite : Un=U0+nr
Donc : a. Un= 5+(-1)n
U8= 5+(-1)x8 = -3
B. Un= -2+1/2n
U8= -2+1/2x8 = 2
C. Un= 3+(-5/4)n
U8= 3+(-5/4)x8= -7
D. Un= n éme terme = U1+(n-1)r
U8= 1+(8-1)x2= 15

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