Question

Sucesiones y progresiones
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Answer 1

Explicación:

1.

$s = 3n + 3 {n}^{2} = 3(n \times (n + 1))$

$a1 = 6 \: \\ d = 6$

$an = 6 + 6 \times (n - 1)$

$a7 = 6 + 6 \times (7 - 1) = 6 + 36 \\ a7 = 42$

2.

$s = n \times (3n + 1) \\ s = 3(n \times (n + \frac{1}{3} ))$

$s = n \times (3n + 1) \\ s2 = 2 \times \: a1 + d = 14 \\ s3 = 3 \times a1 + 3d = 30$

$a1 = 4 \\ d = 6 \\ rspta = 6 - 4 = 2$