Question

calcule a soma dos 35 termo d PA(20,30..)

Answer 1

Sn= ( a1+an)n   
             2
logo preciso saaber quem  é o an
an= a1+(n-1)R
a35= 20+(35-1)10
A35= 20+340
A35=360

S35= (20+360)35    
               2
S35= (380.35) :2
s35= 13.300:2
S35=6.650