4 - Winston-Salem/Forsyth County Schools



4.1 Triangles and Angles

Triangle: a figure formed by three segments joining three noncollinear points. It can be classified by its sides and by its angles.

Classification by Sides

Equilateral Isosceles Scalene

3 congruent sides at least 2 congruent sides no congruent sides

Classification by Angles

Acute Equiangular Right Obtuse

3 acute angles 3 congruent angles 1 right angle 1 obtuse angle

Vertex: each of three points joining the sides of a triangle.

A, B, and C are vertices of triangle ABC. A

B C

Adjacent sides: two sides sharing a common vertex. AB and BC share vertex B.

Right and Isosceles Triangles

Right Triangle Isosceles Triangle

hypotenuse

leg leg leg

leg

base

Triangle Sum Theorem:

The sum of the measures of the interior angles of a triangle is 180*.

m ................
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