This document defines and describes different types of triangles based on side lengths and angles. It explains that a triangle has three sides and three angles that always sum to 180 degrees. Scalene triangles have three unequal sides, isosceles triangles have two equal sides, and equilateral triangles have three equal sides. Right triangles contain one 90 degree angle. The document provides an example of using the triangle angle sum rule to calculate the measure of an unknown angle given the measures of the other two angles.

1. Triangles and Angles

2. A triangle is a plane
figure bounded by three
straight lines. A scalene
triangle has three sides
of unequal lengths, an
isosceles triangle has
two equal sides, and an
equilateral triangle has
three equal sides

3. An isosceles triangle
is a triangle with at
least two sides of
the same length.

4. A scalene triangle
has three sides of
unequal lengths.

5. An equilateral
triangle is a triangle
whose three sides
are of equal length.
Hence, it is also
equiangular with
respect to angles.

6. A right triangle is a
triangle in which one
angle is a right angle.
The side opposite the
right angle is called the
hypotenuse; the two
adjacent sides, the
legs.

7.  Always remember in calculating the angles of
any triangles, the sum of its angles is always
equals to 180°.
 Apply the rule:
θA + θB + θC= 180°
where:
The symbol ‘θ’ use for naming
angles and the capital letters are names of a
triangle.

8.  Example: We want to calculate θA of
triangle ABC. Given: θB= 114°, θC= 25°.
 We apply the rule θ A + 114° + 25° = 180°.
 From this, we have the calculations: θA +
139° = 180° and θA = 180° - 139° = 41°.

9. The End
Thanks for Watching
Prepared by:
Cris Jan M. Batingal BSEd-III