Question

哪有不瘋的

想求這題的詳解
謝謝🙇‍♀️

計算題:
1.有一等比数列,第3項為108,第5項為768,則公比=?首項=?
A₂ = a₁ +8² = 108
as = a₁+4=768
14-12
r² (r²-1)

Answer 1

qn

a₃ = a₁r² = 108
a₅ = a₁r⁴ = 768
下式除以上式
r² = 64/9
r = ±8/3

a₁ = a₃/r²
= 108 × (9/64)
= 243/16