Question

va rog cat mai corect , dau coroana

Answer 1

Răspuns:

Explicație pas cu pas:

Sn = 2*(a1 + an)/2

a1 = 1

a3 = 5

S3 = 3*(1 + 5)/2 = 3*6/2 = 9

Answer 2

$\it S_3=\dfrac{(a_1+a_3)\cdot3}{2}=\dfrac{(1+5)\cdot3}{2}=\dfrac{6\cdot3}{2}=9$