

Course 1, Unit 6  Patterns in Shape
Overview
The intent of this unit is to review, deepen, and extend students' understanding
of two and threedimensional shapes, their representations, their properties,
and their uses. The fundamental idea of this unit is one of shape—what
gives shapes their form and how the shape of an object often influences
its function. The unit provides an introduction to mathematical reasoning
as a way to discover or establish new facts as consequences of known
or assumed facts. As such, the unit lays the groundwork for ideas of
mathematical argument or proof that will be developed formally in Courses
2, 3, and 4. The focus here is on careful visual reasoning, not on
formal proof.
Key Ideas from Course 1, Unit 6

The Triangle Inequality: This relationship among the lengths
of the sides of a triangle is developed on pages 363364.
(The quadrilateral analog to this inequality is developed on page 365.)

Conditions that are sufficient for testing congruence of triangles: sidesideside,
sideangleside, and anglesideangle are developed on pages 369371.

The Pythagorean Theorem: If the lengths of the sides of a
right triangle are a, b, and c, with the side
length c opposite the right angle, then a^{2} + b^{2} = c^{2}.
For example:
(This relationship is taught in most middle school classes. It
was reviewed in Course 1 Unit 1 on page 50 and
used for various review tasks in this course.)

The converse of a statement: The converse of an ifthen statement
reverses the order of the two parts of the statement. For example,
the converse of the Pythagorean Theorem is: If the sum of the squares
of the lengths of two sides of a triangle equals the square of the
length of the third side, then the triangle is a right triangle.
The converse of the Pythagorean Theorem has a very practical use
 that of ensuring that a right angle is formed. (See page 380
Problem 3.)

Visualize and represent two and threedimensional shapes: Students
build models of polyhedra and consider properties of polygons and
polyhedra such as symmetry and rigidity.

Polygon: closed figures in a plane formed by connecting line
segments endpointtoendpoint with each segment meeting exactly two
other segments. For example, three sides would make a triangle, four
a quadrilateral, five a pentagon, as below.

Polyhedron (plural  polyhedra): A threedimensional counterpart
of a polygon, made up of a set of polygons that encloses a single
region of space. Exactly two polygons (faces) meet at each edge and
three or more edges meet at each vertex. (See the examples below
and page 429.)

Name, analyze, and apply properties of polygons and polyhedra: Polygons
are frequently classified by the number of sides they have (page 400).
For example, a 10sided polygon is called a decagon. Characteristics
of pyramids, prisms, cylinders, and cones are developed in Lesson
3 (pages 424431).
