Triangle is a simple closed curve made up with 3 lines segment. it have 3 vertex, 3 side and 3 angle. In a **triangle ABC**, the side are AB, BC, CA. Angles are ∠BAC, ∠ABC, ∠BCA. Vertices are A,B,C. In the above triangle the side opposite to the vertex A is BC. please try to say the opposite side of other vertex.

**Based on side** triangle can classifieds in to Scalene ( all three sides are unequal), Isosceles (2 sides are same), And Equilateral triangle (3 side are same).

**Based on Angles** Triangle can classifieds in to Acute-angle, Obtuse-angle, and Right angle triangle. see page 113.

Medians of triangle

* A median is the line segment between a vertex and the midpoint of the opposite side. *A triangle can be 3 medians. If we cut a triangle in a sheet of paper we can fold each of its sides and can be find the midpoint of each side. see (P114) for think and discuss.

**Altitude of a triangle**

It is nothing but the height of the triangle. **It is the line segment between the base and opposite vertex. **See (P115) for think and discuss. See (P116) for exercise.