Question

Jika u1 + u2 +... adalah deret gemetri dengan u1 = x^-2, u5 = x^2 dan u6 = 8 maka nilai u7 adalah

mohon bantuaan

Answer 1

U1 = a
a = x⁻²
Un =a r^(n-1)

U5 = a r⁵⁻¹
U5 = ar⁴
x² = x⁻²r⁴
r⁴ = x² / x⁻²
r⁴ = x⁴
r = x

U6 = ar⁶⁻¹
= ar⁵

8 = x⁻²(x⁵)
8 = x⁻²⁺⁵
8 = x³
x = ∛8
x = 2

r = 2
a = 2⁻²
a = 1 / 2²
a = 1/4

U7 = ar⁷⁻¹
= ar⁶
= (1/4)2⁶
= (1/4) . 64
= 16

Answer 2

U₁ = x⁻²
U₅= U₁ . r⁴
x²= x⁻²r⁴
x⁴ = r⁴
r = x
r=U₆/U₅
r = 8/r²
r³ = 8
r = 2
U₇ = U₁ . r⁶
U₇ = 2⁻² . 2⁶= 2⁴
U₇ = 16