Download Lecture 3 - CSUN.edu

Math 310 / CSUN / Fall 2009
Instructor: Dr. B. Onzol
Time: 1h 15min.
Lecture 3
1. Triangles
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School definition
The sum of the angles of a triangle can be demonstrate by:
o Picture proof
o Measure and add the angles
o Studying right triangles.
Exterior angles
2. Symmetry and triangles
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Line of symmetry
Rotational symmetry.
3. Types of triangles
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Classification by angles:
o Acute triangle
o Right triangle
o Obtuse triangle
Classification by sides, or by their lines of symmetry:
o Scalene triangle
o Isosceles triangle
o Equilateral triangle.
4. Properties of equilateral and isosceles triangles.
5. Important fact in geometry.
1. In any triangle, the sum of the measures of the interior angles is 180.
2. When one angle of a triangle is a right angle, the measure of the other two angles adds up to 90.
3. Every triangle has 3 pairs of exterior angles.
4. At each vertex, interior and exterior angles are supplementary.
5. The measure of each exterior angle of a triangle is the sum of the opposite interior angle.
6. Homework: study section 2.2 and 2.3. Solve problems 1,2,4, and 8, from homework set 6, also
problems 1,5,6,7 from homework set 7.