Barisan dan Deret Kelas XI

a=p^-2
r=U2/U1= p^2x / p^-2 = P^(2x- -2) =P^ (2x+2)

U10= ar^10-1
U10=ar^9
p^88 = P^-2 (P^2x+2)^9
P^88 = P^-2 P^18x+18
P^88 = P^18x+16
coret p
88=18x+16
72=18x
x=4 (E)

Matematika
Bab : Barisan dan Deret
Materi : Deret geometri

Diketahui:
U1 : a = p⁻² ................ (1)
U2 : a.r = p²ˣ ............... (2)
U10 : a.r⁹ = p⁴⁸ ............ (3)

Ditanya:
Nilai x = ??

Penyelesaian:
Subtitusikan 1 ke 2 ↓↓↓
a.r = p²ˣ
p⁻².r = p²ˣ
r = p²ˣ / p⁻²
r = p²ˣ⁻⁽⁻²⁾
r = p²ˣ⁺² ...................... (4)

Subtitusikan 1 dan 4 ke 3 ↓↓↓
a.r⁹ = p⁴⁸
p⁻².p⁹⁽²ˣ⁺²⁾ = p⁸⁸
p⁻².p¹⁸ˣ⁺¹⁸ = p⁸⁸
p⁻²⁺¹⁸ˣ⁺¹⁸ = p⁸⁸
p¹⁸ˣ⁺¹⁶ = p⁸⁸ ................. (coret "p")
18x + 16 = 88
18x = 88 - 16
18x = 72
x = 72 / 18
x = 4 (E)