Chapter 7 - Section 7.2 - Concurrence of Lines - Exercises - Page 335: 19

Draw the altitudes of the triangle.

This is the same as with problem 18, except now it is an obtuse triangle, so the altitudes for the sides opposite the acute angles will have to be extended. First, draw an obtuse triangle. Next, draw the altitudes of the triangle. The orthocenter of the triangle is the intersection of three altitudes.