Question

Calcule a soma dos quinze primeiros termos da PA (-45,-41,-37,-33,...)

Answer 1

a1= -45
an=?
n=15
r= 4
Sn=?

An= a1+(n-1).r
An= -45 +(15-1).4
An= -45 + 14.4
An= -45+56
An= 11


SN= (a1+An).n/2
SN= (-45+11).15/2
SN= -34.15/2
SN= -510/2
sn= -255.


Espero ter ajudado! ;)