1. Warm Up
The lengths of three sides of a triangle are given. Classify the triangle.
1. 12, 12, 12
2. 18, 10, 14
3. 15, 15, 26
equilateral
scalene
isosceles

2. Learn to identify, classify, and compare quadrilaterals.

3. Vocabulary quadrilateral parallelogram rectangle rhombus square
trapezoid

4. A quadrilateral is a plane figure with four sides and four angles.
Five special types of quadrilaterals and their properties will be shown in this lesson. The same mark on two or more sides of a figure indicates that the sides are congruent.

5. Opposite sides are parallel and congruent
Opposite sides are parallel and congruent. Opposite angles are congruent.
Parallelogram
Parallelogram with four right angles.
Opposites sides are parallel and congruent.
Rectangle

6. Parallelogram with four congruent sides. Opposite angles are congruent.
Rhombus
Rectangle with four congruent sides. All angles are right angles.
Square

7. Quadrilateral with exactly two parallel sides
Quadrilateral with exactly two parallel sides. May have two right angles.
Trapezoid

8. Additional Example 1A: Naming Quadrilaterals
Give the most descriptive name for each figure.
There are two parallel sides. There are no congruent angles.
The figure is a quadrilateral and a trapezoid.
Trapezoid is the most descriptive name.

9. Additional Example 1B: Naming Quadrilaterals
Give the most descriptive name for each figure.
There are four congruent sides and four right angles.
The figure is a quadrilateral, a parallelogram, and a rectangle.
Rectangle is the most descriptive name.

10. Additional Example 1C: Naming Quadrilaterals
Give the most descriptive name for each figure.
The figure is a plane figure with three congruent sides.
Equilateral triangle is the most descriptive name.

11. Additional Example 1D: Naming Quadrilaterals
Give the most descriptive name for each figure.
There are four congruent sides, and opposite angles are congruent.
The figure is a quadrilateral, parallelogram, and rhombus.
Rhombus is the most descriptive name.

12. There are two parallel sides. There are no congruent angles.
Check It Out: Example 1A
Give the most descriptive name for each figure.
There are two parallel sides. There are no congruent angles.
The figure is a quadrilateral and a trapezoid.
Trapezoid is the most descriptive name.

13. There are two pairs of congruent sides.
Check It Out: Example 1B
Give the most descriptive name for each figure.
There are two pairs of congruent sides.
The figure is a quadrilateral and parallelogram.
Parallelogram is the most descriptive name.

14. This figure is an isosceles triangle.
Check It Out: Example 1C
Give the most descriptive name for each figure.
The figure is a plane figure with three sides, two of them being congruent.
This figure is an isosceles triangle.

15. There are four congruent sides.
Check It Out: Example 1D
Give the most descriptive name for each figure.
There are four congruent sides.
The figure is a quadrilateral and parallelogram.
Parallelogram is the most descriptive name.

16. You can draw a diagram to classify quadrilaterals based on their properties.

17. Additional Example 2: Classifying Quadrilaterals
Complete each statement.
A. A rectangle can also be called a ________.
B. A parallelogram cannot be a __________. ?
A rectangle has opposite sides that are parallel; it can be called a parallelogram. ?
A parallelogram has opposite sides that are parallel; it cannot be called a trapezoid.

18. Check It Out: Example 2
Complete each statement.
A. A rhombus with four right angles is a ________.
B. A trapezoid has exactly _______ parallel sides, and may have _____ right angles. ?
A rhombus has four congruent sides, and the opposite sides are parallel. If it has four right angles, then it is a square. ? ?
A trapezoid is a quadrilateral with exactly two parallel sides and it may have two right angles.

19. Lesson Quiz
Complete each statement.
1. A quadrilateral with four right angles is a _________.
2. A parallelogram with four right angles and four congruent sides is a _______.
3. A figure with 4 sides and 4 angles is a ______.
4. Give the most descriptive name for this quadrilateral. ?
square or rectangle ?
square ?
quadrilateral
trapezoid