Question 9
A sequence is formed by the following rules: $s_1=a$, $s_2=b$ and $s_{n+2}=s_{n+1}+(-1)^ns_n$ for all $n\ge1$. If $a=3$ and $b$ is an integer less than $1000$, what is the largest value of $b$ for which $2015$ is a member of the sequence? Justify your answer.
Written reasoning is required. The reference answer is not an automatic assessment of a student proof.
Written reasoning is required. The reference answer is not an automatic assessment of a student proof.