13. In triangle \(A B C , B C = 12 \mathrm {~cm}\) and \(\cos A \hat { B } C = \frac { 2 } { 3 }\).
The length of \(A C\) is 2 cm greater than the length of \(A B\).
- Find the lengths of \(A B\) and \(A C\).
- Find the exact value of \(\sin B \hat { A } C\). Give your answer in its simplest form.