Question

Am nevoie de rezolvare urgent

Answer 1

Explicație pas cu pas:

5.

$n = 1 \implies S_{1} = a_{1}$

$S_{1} = 1^{2} + 2 \cdot 1 = 1 + 2 = 3$

$\implies a_{1} = 3$

$n = 2 \implies S_{2} = a_{1} + a_{2} = 3 + a_{2}$

$S_{2} = 2^{2} + 2 \cdot 2 = 4 + 4 = 8$

$\implies a_{2} = 8 - 3 = 5$

$r = a_{2} - a_{1} = 5 - 3 = 2$

$\implies (a_{n})_{n \geqslant 1} \ ; \ a_{1} = 3 \ ; \ r = 2$