Chapter 9 Quadratic Relations and Conic Sections - 9.1 Apply the Distance and Midpoint Formulas - 9.1 Exercises - Skill Practice - Page 617: 13

$$\left(5,\:\frac{9}{2}\right)$$

Using the distance formula, we find: $$\sqrt{\left(15-\left(-5\right)\right)^2+\left(8-1\right)^2}\\ \sqrt{449}$$ Using the midpoint formula, we find: $$\left(\frac{15-5}{2},\:\frac{8+1}{2}\right)\\ \left(5,\:\frac{9}{2}\right)$$