soal mtk kelas 12 ipa

Jumlah n suku pertama suatu deret geometri dirumuskan dengan Sn=23n-1. Rasio deret tersebut adalah….
A. 8
B. 7
C. 4
D. -1/8
E. -8

Default Asked on January 6, 2016 in Matematika.
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2 Answer(s)

Sn = 23n – 1

U1 = S1 = 23 (1) – 1 = 22
S2 = 23(2)-1 = 45
S2 = U1 + U2
45 = 22 + U2
U2 = 45 – 22
U2 = 23

r = U2/U1 = 23/22

tapi masih ragu kak.. itu bener 23n – 1 atau 23n– 1
kalau ada fotonya di attach aja kak

Train Answered on January 6, 2016.
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Maksudmu 2^3n-1 mungkin

S1=U1= 2^3.1-1= 2^2 = 4
S2= 2^3.2-1 = 2^5 = 32
U2= 32-4 = 28

rasio = U2/U1 = 28/4 = 7 (B)

Train Answered on January 9, 2016.
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