1. **State the problem:** Find the value of $A$ such that the slope from point $(5,8)$ to point $(A,4)$ is undefined. 2. **Recall the formula for slope:** The slope $m$ between two points $(x_1,y_1)$ and $(x_2,y_2)$ is given by: $$m = \frac{y_2 - y_1}{x_2 - x_1}$$ 3. **Understand when slope is undefined:** The slope is undefined when the denominator is zero, i.e., when $x_2 - x_1 = 0$. 4. **Apply to the given points:** Here, the points are $(5,8)$ and $(A,4)$. The slope is undefined if: $$A - 5 = 0$$ 5. **Solve for $A$:** $$A = 5$$ **Final answer:** The value of $A$ is $5$ so that the slope from $(5,8)$ to $(A,4)$ is undefined.