Question

Calcule a soma dos 21 termos iniciais da P.G (1,3, ...).

Answer 1

a1 = 1
a2 = 3
q = 3/1  =3 
n = 21

S21 =  a1 .( qⁿ  - 1)/ ( q - 1)
S21 = 1 ( 3²¹  - 1 )/( 3 - 1)
S21 = ( 104603532 - 1)/2
S21 = 104603531 / 2
S21 = 5230176,5 ****

Answer 2

a1=1
a2=3
q=3
n=21

s21=a1*(q^n - 1 ) / ( q - 1 )

s21= 1 ( 3^21 - 1 ) /( 3 - 1 )

s21= ( 104603532 - 1 ) / 2

s21= 104603531 / 2

s21= 5230176,5.