This Instructional Activity is a part of the Lesson 3, Unit 5, Grade 6. Students need the triangle template found at the end of the lesson and a ruler to complete this example. To save class time, cut out the triangles ahead of time. The height of a triangle does not always have to be a side of the triangle. The height of a triangle is also called the altitude, which is a line segment from a vertex of the triangle and perpendicular to the opposite side.