Question

calcule a soma das seguintes PA(4,7,10,13,16,19)

Answer 1

$S_{n}$ = $\frac{(a1+an).r}{2}$

a1=4 r=3 an=19
$\frac{(4+19).r}{2}$

$\frac{23.3}{2}$

$\frac{69}{2}$

$S_{n}= 34,5$