Question

calcule a soma dos 12 primeiros termos da PG (5, 10, 20, ...).

Answer 1

$\largeA ~soma ~dos ~12 ~primeiros ~termos ~da ~PG ~ \Rightarrow ~ S12 =20475$

Encontrar a razão da PG.

$q = \dfrac{a2}{a1} \\\\\\q = \dfrac{10}{5} \\\\\\q = 2$

Soma dos termos.

$Sn = \dfrac{a1 ~. ~(q^n - 1)}{q - 1} \\\\\\S12 = \dfrac{5 ~. ~(2^{12} - 1)}{2 - 1} \\\\\\S12 = \dfrac{5 ~. ~(4096 - 1)}{1} \\\\\\S12 = \dfrac{5 ~. ~(4095)}{1} \\\\\\S12 =20475$

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