The Fibonacci sequence is defined by a1=1, a2, an=an−1+an−2 for n > 2. Find an+1an for n = 1, 2, 3, 4, 5.
an=an−1+an−2 for n > 2, a = 1
⇒a3=a3−1+a3−2=a2+a1=1+1=2
⇒a4=a4−1+a4−2=a3+a2=2+1=3
⇒a5=a5−1+a5−2=a4+a3=3+2=5
⇒a6=a6−1+a6−2=a5+a4=5+3=8
∴ For n = 1
an+1an=a2a1=11=1
For n = 2
a3a2=21=2
For n = 3
a4a3=32=1.5
For n = 4 and n = 5
a5a4=53 and a6a5=85
∴ The required series is 1,2,32,53,85,……