已知数列{b1}是等比数列⑴若b1=24,q=1/5,求bn.⑵若b3=3,b6=24,求q,b0.⑶若b1=-1/8，b2=一4，求b1，bn

Question

已知数列{b1}是等比数列⑴若b1=24,q=1/5,求bn.⑵若b3=3,b6=24,求q,b
0.⑶若b1=-1/8，b2=一4，求b1，bn

Answer 1

bn=b1.q^(n-1)
(1)
bn = 24.(1/5)^(n-1)
(2)
b3=3
b1q^2 =3 (1)
b6=24
b1q^5=24 (2)
(2)/(1)
q^3=8
q=2
from (1)
4b1=3
b1=3/4
(3)
b1=-1/8
q=b2/b1=(-4)/(-1/8)=32
bn =b1.q^(n-1)
= -(1/8).32^(n-1)