Chapter 5 - Relationships Within Triangles - 5-4 Medians and Altitudes - Practice and Problem-Solving Exercises - Page 313: 14

The intersection of the two lines: (2,0)

$\overline{ab}$ is horizontal, so the line containing the altitude is vertical and contains C(4,2). It's equation is x = 4. BC is vertical, so the line containing the altitude is horizontal and contains A(0,0). It's equation is y = 0. The intersection of these two lines is (4,0).