Q: Find all cosets of H = {0,3} in (ℤ₆,+). H = {0,3} ≤ ℤ₆ ✓ (subgroup!). 0+H = {0,3} = H. 1+H = {1,4}. 2+H = {2,5}. 3+H = {3,0} = H (repeat!). Cosets: {0,3}, {1,4}, {2,5} - PARTITION ℤ₆! (3 cosets, each size 2: 3×2 = 6 ✓!)