Explanation:
Recursive Rule would get by just carefully analysing the pattern and common difference.
a1 = 0 ,
d = a2-a1 ==> d = -3-0 ==> d = -3 ...(common difference)
so here, an would be,
an = a1 + (n-1) d
==> an = 0 + (n-1)(- 3)
==> an = -3(n-1)
==> an = -3n+3
so the final answer is [an = -3n + 3 ]