1. An Introduction to Quadrilaterals
by Carol Edelstein

2. Polygon – a closed, straight-sided, plane figure.
Definition
Polygon – a closed, straight-sided, plane figure.

3. Angle – two rays that meet at a common end point.
Definition
Angle – two rays that meet at a common end point.

4. Definition
Degree – a unit of measurement of an angle, represented by the symbol º.
90º

5. Definition
Diagonal – a line segment joining two non-adjacent vertices of a polygon.

6. Quadrilateral – a polygon with 4 angles and 4 straight sides.
Definition
Quadrilateral – a polygon with 4 angles and 4 straight sides.

7. Special Quadrilaterals
Parallelograms – opposite sides are parallel and congruent.
Rectangles – a parallelogram with all angles 90°.
Squares – a rectangle with all sides equal .
Rhombus – a parallelogram with all sides equal.
Trapezoid – one set of sides are parallel.

8. Venn Diagram Persective of Quadrilaterals
Quadrilaterals – 4 sided polygon
Parallelograms
(opposite sides are parallel and congruent).
Trapezoids
(one set of parallel sides)
Rhombus
Rectangle
Square

9. Quadrilateral Family trapezoid parallelogram rectangle rhombus
square

10. Property of Quadrilaterals
The sum of all the interior angles equals 360º.

11. Property of Quadrilaterals
Why is the sum 360º ?
Well, if you choose a vertex you can only draw one diagonal. This one diagonal “splits” the quadrilateral into two triangles.
Since the sum of the internal angles of a triangle are 180 degrees, a quadrilateral has 360 degrees (2 x 180 º ).

12. Property of Quadrilaterals
The sum of all the interior angles equals 360º degrees.
65º
65º
115º
65º
115º
115º +
65º
115º
360º

13. What is the missing angle?
90º
90º
90º
90º
90º +
90º ?
90º ?
360º

14. What is the missing angle?
70º
70º
70º
70º
110º ?
110º
110º ? +
360º

15. What is the missing angle?
65º
65º ?
65º
115º
65º
115º
115º + ?
360º

16. What is the missing angle?
60º
81º
104º ?
104º
115º
60º
81º + ?
360º

17. Congratulations and good job!
Now you know that…
A quadrilateral is a 4-sided polygon.
There are many types of quadrilaterals.
Classification depends on how many sets of sides are parallel, the length of the sides and the measure of the interior angles.
The sum of the interior angles of a quadrilateral is 360º.