Find the value(s) for which the rational expression is undefined. \[ \frac{8}{x+9} \]

Step 1 ：Find the value(s) for which the rational expression is undefined. The expression is \(\frac{8}{x+9}\).

Step 2 ：To find the value for which the expression is undefined, we need to solve the equation \(x + 9 = 0\).

Step 3 ：Subtract 9 from both sides of the equation to isolate x.

Step 4 ：The solution to the equation \(x + 9 = 0\) is \(x = -9\).

Step 5 ：This means that the rational expression is undefined when \(x = -9\).

Step 6 ：Final Answer: The rational expression is undefined when \(x = \boxed{-9}\).