Question

Geometric Sequences
http://puu.sh/aWG4v/cf6160522c.jpg

Answer 1

I don't understand, the lesson always said, the domain can only be n >=1, so how am I supposed to find n = 0 if it n = 0 goes against the rules of sequences.

Answer 2

a2=10
a3=5
a4=2.5
a5=1.25

so
q=a2/a1=a3/a2=a4/a3 =5/10 =2.5=5 ..=1/2
then
a(n)=a1 q^(n-1)

a2=a1 q =1/2 a1 ----> a1=20

now a(n)=20 (1/2)^(n-1)
or a(n)=10 (1/2)^(n-2)

Answer 3

Thanks so much!