_______ is an altitude in the exterior of the given triangle XYZ.

 

We have been given a triangle XYZ that is obtuse angled triangle. 

This is because the ∠XZY is obtuse.

We know that a line that is drawn perpendicularly from one vertex of a triangle to the opposite side is defined as the altitude of a triangle. 

Also, the altitudes of an obtuse angled triangle lie in the exterior of the triangle. 

Here, the line YL is drawn perpendicularly from vertex Y of a triangle XYZ to the opposite side XZ. 

Therefore, YL is an altitude in the exterior of the triangle XYZ.