Question

determine a soma doa termos (3,11,19,..,119)

Answer 1

razão = 8
fórmula do termo geral : an = a1 + (n - 1).razão
119  = 3 + (n - 1).8
119-3= (n-1)8
116=8n -8
116+8 = 8n
224 = 8n
n = 28
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Sn = (a1+an)n/2= (3+119)28/2= (3+119)14 = 124 . 14 = 1736