Question

quantos termos tem a P.A (4,7,10...,157)

Answer 1

a₁ = 4
r = 3
n = ?
an = 157
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an = a₁ + (n-1).r
157 = 4 + (n-1).3
157 - 4 = 3(n-1)
153 = 3(n-1)
(n-1) = 153/3
n - 1 = 51
n = 51 + 1

n = 52 termos

Answer 2

an = a1 + (n-1) . r
157 = 4 + (n-1) . 3
157 = 4 + 3n - 3
3n = 157 -  4 + 3
3n = 156
n = 156/3
n = 52