Bantu nomor 14,15 dong

Bantu nomor 14,15 dong

Jawaban Terkonfirmasi

14) a = 1/9
r = 3

Un = a $r^{n-1}$
81 = 1/9 . $3^{n-1}$
$3^{n-1}$ = 81 : 1/9
$3^{n-1}$ = 81 × 9/1
$3^{n-1}$ = 729
$3^{n-1}$ = $3^{6}$
$3^{7-1}$ = $3^{6}$
n = 7

Jadi, jawabannya B. 7.

15) U2 = 1/2
U6 = 8

$r^{6-2}$ = U6/U2
$r^{4}$ = 8 : 1/2
$r^{4}$ = 8 × 2
$r^{4}$ = 16
r = 2

U2 => a . r = 1/2
a . 2 = 1/2
a = 1/2 : 2
a = 1/2 . 1/2
a = 1/4

U10 = a . $r^{9}$
= 1/4 . $2^{9}$
= 1/4 . 512
= 128

Jadi, jawabannya adalah C.