8.4 Rectangles. Objectives Recognize and apply properties of rectangles Determine whether parallelograms are rectangles.

8.4 Rectangles8.4 Rectangles

Objectives

Recognize and apply properties of rectangles

Determine whether parallelograms are rectangles

Rectangles

A rectangle is a parallelogram with four right angles.

Rectangles Since rectangles are parallelograms, they

have all their properties:

Opposite sides are || and ≅.Opposite s are .≅Consecutive s are supplementary.Diagonals bisect each other.

In addition, there exists Theorem 8.13 which states if a is a rectangle then the diagonals are ≅.

Quadrilateral RSTU is a rectangle. If and find x.

Example 1:

The diagonals of a rectangle are congruent,

Definition of congruent segments

Substitution

Subtract 6x from each side.

Add 4 to each side.

Answer: 8

Example 1:

Answer: 5

Quadrilateral EFGH is a rectangle. If and find x.

Your Turn:

Quadrilateral LMNP is a rectangle. Find x.

Example 2a:

Angle Addition Theorem

Answer: 10

Substitution

Simplify.

Subtract 10 from each side.

Divide each side by 8.

Example 2a:

Quadrilateral LMNP is a rectangle. Find y.

Example 2b:

Since a rectangle is a parallelogram, opposite sides are parallel. So, alternate interior angles are congruent.

Alternate Interior Angles Theorem

Divide each side by 6.

Substitution

Subtract 2 from each side.

Simplify.

Answer: 5

Example 2b:

Quadrilateral EFGH is a rectangle.

a. Find x. b. Find y.

Answer: 11 Answer: 7

Your Turn:

Kyle is building a barn for his horse. He measures the diagonals of the door opening to make sure that they bisect each other and they are congruent. How does he know that the corners are angles?

We know that A parallelogram with congruent diagonals is a rectangle. Therefore, the corners are angles.

Answer:

Example 3:

Max is building a swimming pool in his backyard. He measures the length and width of the pool so that opposite sides are parallel. He also measures the diagonals of the pool to make sure that they are congruent. How does he know that the measure of each corner is 90?

Answer: Since opposite sides are parallel, we know thatRSTU is a parallelogram. We know that . A parallelogram with congruent diagonals is a rectangle. Therefore, the corners are

Your Turn:

Quadrilateral ABCD has vertices A(–2, 1), B(4, 3), C(5, 0), and D(–1, –2). Determine whether ABCD is a rectangle using the Slope Formula.

Method 1: Use the Slope Formula, to see if

consecutive sides are perpendicular.

Example 4:

Answer: The perpendicular segments create four right angles. Therefore, by definition ABCD is a rectangle.

quadrilateral ABCD is a parallelogram. The product of the slopes of consecutive sides is –1. This means that

Example 4:

Method 2: Use the Distance Formula,

to determine whether opposite sides are congruent.

Example 4:

Since each pair of opposite sides of the quadrilateral have the same measure, they are congruent. Quadrilateral ABCD is a parallelogram.

Example 4:

The length of each diagonal is

Answer: Since the diagonals are congruent, ABCD is a rectangle.

Find the length of the diagonals.

Example 4:

Quadrilateral WXYZ has vertices W(–2, 1), X(–1, 3), Y(3, 1), and Z(2, –1). Determine whether WXYZ is a rectangle using the Distance Formula.

Your Turn:

Answer: we can conclude that opposite sides of the quadrilateral are congruent. Therefore, WXYZ is a parallelogram. Diagonals WY and XZ each have a length of 5. Since the diagonals are congruent, WXYZ is a rectangle by Theorem 8.14.

Your Turn:

Assignment

Pre-AP GeometryPre-AP GeometryPg. 428 #10 - 32, 36, 42

Geometry:Geometry:Pg. 428 #10 - 29