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Geometry Lesson: Triangles and Quadrilaterals
SOL: 6.14- The student will identify, classify, and describe the
characteristics of plane figures, describing their similarities,
differences, and defining properties.
Today’s Objectives:
1.
Warm Up Activity
2.
Algebra Preview
3.
Lecture
4.
Activity
5.
Lecture
6.
Worksheet
7.
Exit Pass
Activity
Today we will…
Begin our unit on polygons by
exploring the properties and
characteristics of triangles and
quadrilaterals.
If the letter “x” represents the number of sides
of a polygon, find x for these pictures…
Triangles
Definition: A triangle is a
polygon with three sides and
three angles.
Triangles According to Side Length
Equilateral triangle is a triangle where all of the
sides have the same length. Also, this means all
of the angles are the same (60º).
Isosceles triangle is a triangle where only two of
the sides have the same length.
Scalene triangle is a triangle where none of the
sides have the same length.
Examples
Equilateral
Isosceles
Scalene
Triangles According to Angle Measure
Acute triangle is a triangle where all of the angles
are less than 90º
Right triangle is a triangle where one angle is
exactly 90º
Obtuse triangle is a triangle where one of the
angles is more than 90º
Note: The sum of the angles in a triangle is 180º.
Examples
Acute
Obtuse
Right
Where do these triangles belong?
Obtuse
Equilateral
Acute
Scalene
Right
Isosceles
Quadrilaterals
Definition: A quadrilateral is a
polygon with four sides and four
angles. The sum of the angles is
360º.
Four Types of Quadrilaterals
Rectangle
Parallelogram
Square
Rhombus
Definitions
A Rectangle is a quadrilateral with opposite sides
congruent, all angles are right angles, and opposite
sides are parallel.
A Square is a quadrilateral with all sides congruent, all
angles are right angles, and opposite sides are parallel.
Definitions
A Parallelogram is a quadrilateral with opposite sides
congruent, opposite sides parallel and opposite
angles congruent.
A Rhombus is a quadrilateral with all sides
congruent, opposite sides congruent, and opposite
angles congruent.
Exit Pass
Answer these questions on an index card and turn in
once you have finished.
1. Name the 6 categories of triangles.
2. Name the 2 types of quadrilaterals we learned
today where all of the sides are congruent.
3. Draw a scalene right triangle.
4. Are there any questions you still have after
today’s lesson?