Question

calcule a soma dos 25 termo da PA (1,7,13,..)

Answer 1

P.A.

$a_{n}$ = $a_{1}$ + (n - 1) * r

$a_{25}$ = 1 + (25 - 1) * 6

$a_{25}$ = 1 + 24 * 6

$a_{25}$ = 1 + 144

$a_{25}$= 145

Soma dos termos:

$s_{n}$  = $\frac{(a1+an)*n}{2}$

$s_{25}$ = $\frac{(1+145) * 25}{2}$

$s_{25}$  = $\frac{146*25}{2}$

$s_{25}$ = $\frac{3650}{2}$

$s_{25}$ = 1825

Soma dos termos: 1825