A recursive rule for a geometric sequence just states the first term and the common ratio for each number to the next term.
The first term in the sequence is 3. (a₁ = 1st term)
To find the common ratio we can divide a term to the previous term.
3/2 = 1.5 → 1.5 / 3 = 0.5
3/4 = 0.75 → 0.75 / 1.5 = 0.5
3/8 = 0.375 → 0.375 / 0.75 = 0.5
As we can see the common ratio is 0.5
The only answer choice that is correct is [ a₁ = 3; aₙ = 1/2 · aₙ₋₁ ]. This is correct because the first term is 3 and the common ratio is 1/2 (0.5).
Best of Luck!