Problem
Which best describes this sequence? \( 3,6,12,18, \ldots \)
Solution
Step 1 ：1. Find differences: \(6-3=3, 12-6=6, 18-12=6\)
Step 2 ：2. Find second differences: \(6-3=3, 6-6=0\)
Step 3 ：3. Second difference is not constant, so the sequence is neither arithmetic nor geometric.
