Question

quantos termos tem na PA (15,28..........275).

Answer 1

Temos que:

a1 = 15
an = 275
n = ?
r = 28 - 15 = 13

an = a1 + (n-1)r
275 = 15 + (n-1)13
275 - 15 = (n-1)13
260 = (n-1)13
260/13 = n-1
20 = n-1
n = 20 + 1
n = 21

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