Respuesta :

This is an arithmetic series,
so 
S(n) = (n/2)*(a(1)+a(n))
S(25) = (25/2)*(a(1)+a(25))
n=25
a(n) = 3n-2
a(1)= 3*1-2=1
a(1)=1
a(25) = 3*25-2=75-2=73
a(25)=73

S(25) = (25/2)*(1+73)=(25/2)*74=925
S(25)=925

Answer : 925