1. Today, we are going to learn about cross sections
Today, we are going to learn about cross sections. You have looked at cross sections before without even knowing it. Consider when you cut a fruit or vegetable. The “face” of the fruit or vegetable after it is cut represents a cross section of that object.
Thought of the Day

2. Section 12-1 Representations of Three-Dimensional Figures

3. Then
Now
Objectives
You identified parallel planes and intersecting planes in three- dimensional figures.
Investigate cross sections of three dimensional figures.

4. Common Core State Standards
Content Standards
G.GMD.4 – Identify the shapes of two- dimensional cross-sections of three- dimensional objects, and identify three- dimensional objects generated by rotations of two-dimensional objects.
Mathematical Practices
1) Make sense of problems and persevere in solving them.
5) Use appropriate tools strategically.
Common Core State Standards

5. A cross section is the intersection of a solid and a plane
A cross section is the intersection of a solid and a plane. The shape of the cross section formed by the intersection of a plane and a three-dimensional figure depends on the angle of the plane.
Vocabulary

6. Scientists are able to use computers to study cross sections of ancient artifacts and structures. Determine the shape of each cross section of the pyramid below.
Example 3

7. Describe the cross section of the cone.
Example 3

8. Describe the cross section of the cone.
Example 3

9. Describe the cross section of the cone.
Example 3

10. Describe the cross sections of the cylinders.
Example 3

11. Describe the cross sections of the prisms.
Example 3

12. Sketch the cross section from a vertical slice of each figure.
Example 3

13. Consider the sphere. Based on the cross section resulting from a horizontal and a vertical slice of the sphere, make a conjecture about all spherical cross sections.
Example 3

14. p.841 #5 – 7, 15 – 19, 25 – 27
Homework