Question

Given the sequence an defined recursively below, find a4.
a1a2an=1=4=2an−1+an−2

Answer 1

Answer:

  $a_4=22$

Step-by-step explanation:

Maybe you have ...

  $a_1=1\\a_2=4\\a_n=2a_{n-1}+a_{n-2}$

Then ...

  $a_3=2\cdot 4+1=9\\\\a_4=2\cdot 9+4=22$