9. $\frac{1}{2}(m-8)$

Step 1 ：Distribute \(\frac{1}{2}\) to both terms inside the parentheses: \(\frac{1}{2}(m-8) = \frac{1}{2}m - \frac{1}{2}(8)\)

Step 2 ：Simplify the expression: \(\frac{1}{2}m - \frac{1}{2}(8) = \frac{1}{2}m - 4\)

Step 3 ：\boxed{\frac{1}{2}m - 4}