Question

Calcular a soma dos 25 primeiro termos da P.A,(1,7,13...)

Answer 1

$a_25= 1+(25-1) .6 a_25= 1 + 24 . 6 a_25= 1 + 144 a_25= 145$

Answer 2

sn=(a1+an)×n an=1 (25-1)×6 an=144 ----------
2
s25=145×25
________
2
s25= 181,25