## Elementary Geometry for College Students (7th Edition)

We replace $x_{1}$and $y_{1}$ by the coordinates of C and $x_{2}$ and $y_{2}$by the coordinates of D. $d=\sqrt{ (x_{2}-x_{1})^{2}+(y_{2}-y_{1})^{2}}=\sqrt{ (0-(-6))^{2}+(9-1)^{2}}=\sqrt{36+64}=\sqrt{100} = 10$