Question

Determine a soma dos 30 primeiros termos da PA (3,7...)

Answer 1

Resposta:

$a_{n} = a_{1} + (n-1) .r \\a_{30} = 3 + (30-1) .4\\a_{30} = 3 + 29 .4\\a_{30} = 3 + 116\\a_{30} = 119$

$S_{n} = \frac{(a_{1}+a_{n}).n }{2}\\S_{30} = \frac{(3+119).30 }{2}\\\\S_{30} = \frac{122.30 }{2}\\\\S_{30} = 61.30\\S_{30} = 1830$

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