Page 219 - ABCTE Study Guide_Neat

This is a scalene triangle. None of its sides are congruent. That is, they all
have different lengths.

This is an isosceles triangle. Two of its sides are congruent. The two
congruent sides are called the legs and the third side is called the base. In
fact, according to the Isosceles Triangle Theorem, the base angles (those
that are opposite the sides that are congruent) are also congruent. The third
angle is called the vertex angle. The triangle is marked with congruence
symbols to show which parts are congruent.

This is an equilateral triangle. All of its sides are congruent. It is
alsoequiangular, which means that all of its angles are also congruent. Since
the sum of the measures of the angles in a triangle is 180°, and all of the
angles in an equilateral triangle are congruent, then each angle measures
180°÷ 3, or 60°. The triangle is marked with congruence symbols to show
which parts are congruent.

Classifying Triangles By Their Angles

There are three classifications of a triangle according to the measures of its angles: acute, right,
and obtuse.