Section 4-1 Triangles and Angles

triangle A figure formed by three segments jining three noncollinear points.

Triangles are classified by their sides and angles.

Side Classification: Equilateral Triangle: 3 congruent sides Isosceles Triangle: at least 2 congruent sides Scalene Triangle: No congruent sides

Isosceles Triangle Equilateral Triangle Scalene Triangle

Angle Classification: Acute Triangle: 3 acute angles Equiangular Triangle: 3 congruent angles Right Triangle: 1 right angle Obtuse Triangle: 1 obtuse angle

Acute Triangle Right Triangle Obtuse Triangle Equiangular Triangle

When naming a triangle you must be as specific as possible! Name triangles by BOTH sides and angles!

Some Examples: 1. Equilateral Equiangular 2. Obtuse Isosceles

Parts of a triangle: The segments are called the sides of a triangle Each of the three points is a vertex of the triangle Two sides sharing a common vertex are adjacent sides

B A C Sides: Vertices: A, B, C

Parts of a right triangle: Leg: the sides that form the right angle Hypotenuse: the side opposite the right angle (longest side)

Hypotenuse Leg Leg

Parts of an isosceles triangle: When it has only two congruent sides: Leg: two congruent sides Base: the 3rd side

Leg Leg Base