Question

given a=7,a13= 35, find dand S13​

Answer 1

$\large{ \bold{given}}$

$a = 7 \\ \\ t13 = 35$

$\large{ \bold{to \: \: \: find}}$

$s13$

$\large{ \bold{solution}}$

$\large{ \bold{tn = a + (n - 1)d}}$

$t13 = 7 + (13 - 1)d$

$35 = 7 + 12d$

$28 = 12d$

$d = 2.33$

$\large{ \bold{sn = \frac{n}{2} (2a + (n - 1)d}}$

$s13 = \frac{13}{2} (2 \times 7 + (13 - 1)2.33$

$s13 = \frac{13}{2} (14 + 28)$

$s13 = \frac{13}{2} (42)$

$s13 = 13 \times 21$

$\large{ \bold{s13 = 273}}$

PLEASE MARK ME AS BRAINLIST