Question

Calcular a soma dos 15 termos da P.A (-2,1,4,7...) ME AJUDEEEM :)

Answer 1

an= a1+ (n-1)r      (a1= -2, n= 15, r=3 an=?)
an= -2 + (15-1)3
an= -2 + 14×3
an= -2 + 42
an= 40

Sn= (an + a1) × n /2
Sn= (-2 + 40) × 15 /2
Sn= 38×15 /2
Sn= 470 /2
Sn= 235