lim n→∞ an^2+bn+1/3n-2
=lim n→∞ ( an + b + 1/n )/ (3-2/n)
∴ a = 0
lim n→∞ an^2+bn+1/3n-2
= lim n→∞ bn+1/3n-2
= lim n→∞ [b + 1/n]/[3-2/n]
= b/3 = -2
∴ b = -6