The document defines and classifies triangles. It states that a triangle is a three-sided polygon whose interior angles sum to 180 degrees. Triangles are classified based on side lengths as equilateral, isosceles, or scalene, and based on angle measures as acute, right, obtuse, or equiangular. The document provides examples of each type of triangle and states that determining missing angles is an important concept.

1. TRIANGLES

2. POLYGON
- A closed plane figure
made up of line
segments.

3. TRIANGLE
● It is a polygon with three sides
and three angles and with a
total interior angle measure of
180°.
● It can be classified according to
sides or angles.

4. TRIANGLES
ACCORDING TO
SIDES

5. EQUILATERAL TRIANGLE
● Its sides are all congruent.

6. ISOSCELES TRIANGLE
● Two of its sides are congruent.
These sides are called the legs.
The third side is called the
base.

7. SCALENE TRIANGLE
● The measurements of the side
of this triangle are different. No
sides of this triangle are
congruent.

8. TRIANGLES
ACCORDING TO
ANGLES

9. ACUTE TRIANGLE
● All of its angles are acute.

10. RIGHT TRIANGLE
● One of its interior angles
measures exactly 90°.

11. OBTUSE TRIANGLE
● One of its interior angles
measures more than 90° but
less than 180°.

12. EQUIANGULAR TRIANGLE
● All of its angles are congruent.
Each measures 60°.

14. Determine the missing angle.

15. Determine the missing angle.

16. Determine the missing angle.