6.4 6.5 6.6: Quadrilaterals and Their

Properties

Objectives: Be able to use properties of sides and angles of

rhombuses, rectangles, squares, trapezoids and kites.

Be able to use properties of diagonals of rhombuses, rectangles and squares.

Be able to identify quadrilaterals based on limited information

Quadrilaterals

A parallelogram with four congruent sides.

A parallelogram with four right angles.

A parallelogram with four congruent sides, and four right angles.

Corollaries▫Rhombus Corollary: A quadrilateral is a rhombus if and only if it has four congruent sides.

▫Rectangle Corollary: A quadrilateral is a rectangle if and only if it has four right angles.

▫Square Corollary: A quadrilateral is a square if and only if it is a rhombus and a rectangle.

You can use these to prove that a quadrilateral is a rhombus, rectangle or square without proving first that the quadrilateral is a parallelogram.

1) Decide whether the statement is always, sometimes, or never.

A. A rectangle is a square.

B. A square is a rhombus.

Example:

Theorems

Theorem

6.11

A parallelogram is a rhombus if and only if its diagonals are perpendicular.

A parallelogram is a rhombus if and only if each diagonal bisects a pair of opposite angles.

Theorem

6.12

Theorem

6.13

A parallelogram is a rectangle if and only if its diagonals are congruent.

2) Which of the following quadrilaterals have the given property?

All sides are congruent.

All angles are congruent.

The diagonals are congruent.

Opposite angles are congruent.

A.Parallelogram

B.Rectangle

C.Rhombus

D.Square

Examples:

3) In the diagram at the right, PQRS is a rhombus. What is the value of y?

5y - 6

2y + 3

P

S

Q

R

Example:

A trapezoid is a quadrilateral with exactly one pair of parallel sides.

Bases: The parallel sides of a trapezoid.Legs: The nonparallel sides of the trapezoid.

Base

Base

Leg LegBase Angles

Trapezoids

Isosceles Trapezoid: A trapezoid whose legs are congruent.Midsegment: A segment that connects the midpoints of the legs and that is parallel to each base. Its length is one half the sum of the lengths of the bases.

Midsegment

A trapezoid that has congruent legs.

Isosceles Trapezoids

Theorem 6.14

Theorem 6.15

Theorem 6.16

If a trapezoid is isosceles, then each pair of base angles is congruent.

A

D C

B

A B C D

If a trapezoid has a pair of congruent base angles, then it is an isosceles trapezoid. D C

BA

A trapezoid is isosceles if and only if its diagonals are congruent.

A B

CDABCD is isosceles if and only if AC .BD

4) is an isosceles trapezoid with

10 and 95 . Find , ,

, and .

CDEF

CE m E DF m C

m D m F

C

FE

D

95

Example

Theorem 6.17: Midsegment of a trapezoid

The midsegment of a trapezoid is parallel to each base and its length is one half the sums of the lengths of the bases.MN║AD, MN║BCMN = ½ (AD + BC)

NM

A D

CB

The midsegment of a trapezoid is the segment that connects the midpoints of its legs.

Midsegment of a trapezoid

Example:

5) Find the length of the midsegment RT.

Definition

•A kite is a quadrilateral that has two pairs of consecutive congruent sides, but opposite sides are not congruent.

Kite TheoremsTheorem 6.18• If a quadrilateral is a

kite, then its diagonals are perpendicular.

• AC BD

B

C

A

D

Theorem 6.19• If a quadrilateral is a

kite, then exactly one pair of opposite angles is congruent.

• A ≅ C, B ≅ D

B

C

A

D

Example 6) Find the lengths of all four sides of the kite.

12

1220

12

U

X

Z

W Y

Example

7) Find mG and mJ in the diagram at the right.

J

G

H K132° 60°