Orthocenter
An orthocenter is the point of concurrency of the three altitudes.
-Construct a triangle DEF and label vertices 
-Construct the three perpendicular lines from each vertex to the opposite side
.
-Locate the orthocenter with intersect tool 
and label it O
-Construct the three perpendicular lines from each vertex to the opposite side.
-Locate the orthocenter with intersect tool and label it O 
Construct the orthocenter below.
Drag around the vertices of your triangle. What kind of triangle is DEF if the orthocenter falls inside the triangle?
What kind of triangle is DEF if the orthocenter is a vertex of the triangle?
What kind of triangle is DEF if the orthocenter is on the exterior (outside) of the triangle?