Question

Quantos termos tem uma progressão aritmética finita, de razão 3, sabendo-se que o primeiro termo é -5 e o último é 16?

Answer 1

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Answer 2

Fórmula do termo geral da PA

an = a1 + (n - 1) . r

an = 16 ; a1 = -5 ; r = 3

16 = -5 + (n - 1).3

16 + 5 = 3(n - 1)

16 + 5 = 3n - 3

16 + 5 + 3 = 3n

24 = 3n

n = 24/3

n = 8

A progressão aritmética tem 8 termos.