MATHS PROJECTMATHS PROJECTQuadrilateralsQuadrilateralsMATHS PROJECTMATHS PROJECTQuadrilateralsQuadrilaterals
Geometry EOCGeometry EOC
Definition
• A plane figure bounded by four line segments AB,BC,CD and DA is called a quadrilateral.
A B
D C*Quadrilateral
I have exactly four sides.
In geometry, a quadrilateral is a polygon with four sides and four vertices. Sometimes, the term
quadrangle is used, for etymological symmetry with triangle, and sometimes tetragon for consistence
with pentagon.
There are over 9,000,000 quadrilaterals. Quadrilaterals are either simple (not self-
intersecting) or complex (self-intersecting). Simple quadrilaterals are either convex or concave.
Types of Quadrilaterals
• Parallelogram
• Trapezium
• Kite
I have:2 sets of parallel sides2 sets of equal sidesopposite angles equaladjacent angles supplementarydiagonals bisect each otherdiagonals form 2 congruent triangles
Parallelogram
Types of Parallelograms
*RectangleI have all of the properties of the
parallelogram PLUS- 4 right angles
- diagonals congruent
*RhombusI have all of the properties of the
parallelogram PLUS- 4 congruent sides- diagonals bisect
angles- diagonals
perpendicular
*SquareHey, look at me!I have all of the properties of the
parallelogram AND the rectangle AND
the rhombus.I have it all!
Is a square a rectangle?
Some people define categories exclusively, so that a rectangle is a quadrilateral with four right angles that is not a square. This is appropriate for everyday use of the words, as people
typically use the less specific word only when the more specific word will not do. Generally a rectangle which isn't a square is
an oblong.But in mathematics, it is important to define categories
inclusively, so that a square is a rectangle. Inclusive categories make statements of theorems shorter, by eliminating the need for tedious listing of cases. For example, the visual proof that
vector addition is commutative is known as the "parallelogram diagram". If categories were exclusive it would have to be known as the "parallelogram (or rectangle or rhombus or
square) diagram"!
Trapezium
I have only one set of parallel sides. [The median of a trapezium is parallel to the bases and equal to one-half the sum of the
bases.]
Trapezoid Regular Trapezoid
It has two pairs of sides.Each pair is made up of adjacent sides (the sides meet) that are equal in length. The angles are equal where the pairs meet. Diagonals (dashed lines) meet at a right angle, and one of the diagonal bisects (cuts equally in half) the other.
Kite
Angle Sum Property Of Angle Sum Property Of QuadrilateralQuadrilateral
The sum of all four angles of a quadrilateral is
360.. A
B C
D
1
23 4
6
5
Given: ABCD is a quadrilateral
To Prove: Angle (A+B+C+D) =360.
Construction: Join diagonal BD
Proof: In ABD
Angle (1+2+6)=180 - (1)
(angle sum property of )
In BCD
Similarly angle (3+4+5)=180 – (2)
Adding (1) and (2)
Angle(1+2+6+3+4+5)=180+180=360
Thus, Angle (A+B+C+D)= 360
The Mid-Point TheoremThe line segment joining the mid-points of two sides of a triangle is parallel to the third side and is half of it.
Given: In ABC. D and E are the mid-points of AB and AC respectively and DE is joined
To prove: DE is parallel to BC and DE=1/2 BC
1
3
2
4
A
D E F
CB
Construction: Extend DE to F such that De=EF and join CFProof: In AED and CEFAngle 1 = Angle 2 (vertically opp angles)AE = EC (given)DE = EF (by construction)Thus, By SAS congruence condition AED= CEFAD=CF (C.P.C.T)And Angle 3 = Angle 4 (C.P.C.T)But they are alternate Interior angles for lines AB and CFThus, AB parallel to CF or DB parallel to FC-(1)AD=CF (proved)Also AD=DB (given)Thus, DB=FC -(2)From (1) and(2)DBCF is a gm
Thus, the other pair DF is parallel to BC and DF=BC (By construction E is the mid-pt of DF)
Thus, DE=1/2 BC
THE END
