기하학및연습 Greenberg - Euclidean and Non-Euclidean Geometries - Development and History 3e (WHF, 1993) 문제풀이(1-2)

2. Define the following terms line 

a) The triangle AABC formed by three non collinear points A, B,and C. 

> If three non-collinear points are joined by a straight line. then the closed figure formed is called triangle - 

 

b) The vertices sides and angles of DABC.

 > A triangle has three sides, three vertices, and three angles. The sum of the the interior angles of a triangle is always 180° The sum of length of two sides of a triangle is always greater than length of third side

 

c) The sides opposite to and adjacent to a given vertex A of DHBC. 

> The point at which any two sites meet is called a verte. Thus, a triangle has three vertices. The vertices of the triangle PQR are P, Q and R. The side opposite to a Vertex is called a base. 

 

d) Medians of a triangle Csee Figure 1.18)

A median of a triangle is a line segment joining a vertex to the midpoint of the opposite side, thus bisecting that side. Every triangle has exactly three medians, one from each vertex, and they

all Intersect each other at the triangle's centroid.

 

 e) Altitudes of a triangle

 An altitude of a triangle is a line segment through a vertex and perpendicular to lie, forming a right angle with) a line containing the base ( the side opposite the Vertex). This line containing the opposite side is called the extended base of the triangle