Question

calcule a soma dos 15 primeiros termos da P.A(4,9,14,19,...).

por favor me ajudem

Answer 1

R=5

A15=A1+14R

A15=4+14(5)

A15=74


Sn=(A1+A15)N/2

Sn=(4+74)15/2

Sn=78(15)/2

Sn=585

Answer 2

a1=4
r=5
a15= a1+14r
a15=4+14.5= 4+70= 74

S= (4+74).15/2= 78.15/2= 1170/2=585