Download 4.2 Classifying Triangles

4-2 Classifying Triangles
Triangle—a figure formed by the segments whose endpoints are three noncollinear points. The
shape of the triangle depends upon the measures of its angles and the lengths of its sides.
Sides—the segments that form a triangle (or any polygon). AB , BC , and AC arethe sides.
Vertices—the endpoints of the sides. A, B, and C are the vertices
A triangle with vertices A, B, C is called▲ABC, or ▲BCA , or ▲CAB. In this case, order
does not matter.
Classifying triangles by angle measures.
Equiangular triangle –three congruent angles. Each angle in any equiangular triangle is 60°
Acute triangle—has three acute angle. An equiangular triangle is an acute triangle.
Right triangle—has a right angle. A triangle can have only one right angle in it. If it is a right
triangle, there can be no obtuse angle in the triangle.
Obtuse triangle—has one obtuse angle in it. A triangle can have only one obtuse angle in it.
There cannot be a right angle in the triangle when there is an obtuse angle in it.
You can classify a triangle by its sides:
Scalene triangle—has no congruent sides. ▲RTS is scalene
Isosceles triangle—has at least two congruent sides ▲XYZ is isosceles. So is ▲ABC
Equilateral triangle—has three (all) congruent sides ▲ABC is equilateral