## 87 terms · Definitions of terms to know as we encounter them in the text. Make sure you can draw them and know the symbols to indicate them.

### reflectional symmetry

when you can fold a design along a line of symmetry so that all points on one side of the line exactly match all the points on the other side. Also called line or mirror symmetry.

### rotational symmetry

when a design looks the same after you turn it around a point by less than a full circle. The # of times it looks the same as you turn it a full 360 degrees determines the type (3-fold, 5-fold etc.)

### bilateral symmetry

when an object has just one line of reflectional symmetry. (butterfly or human body etc.)

### line

a straight , continuous arrangement of infinitely many points, with infinite length but no thickness, extending forever in two directions. Named by giving the letter names of any two points on the line and by placing the line symbol above the letters.

### plane

has infinite length and infinite width, but no thickness. Named with a script capital letter.

### Coordinate Midpoint Property

if (x1, y1) and (x2, y2) are the coordinates of the endpoints of a segment, then the coordinates of the midpoint are (x1+x2/2, y1+y2/2)

### measure of an angle

the smallest amount of rotation about the vertex from one ray to the other, measured in degrees.

### congruent angles

if and only if two angles have the same measure. You use identical markings to show on a figure.

### angle bisector

a ray is the angle bisector if it contains the vertex and divides the angle into two congruent angles.

### incoming angle (in pool)

is formed by the cushion and the path of the ball approaching the cushion.

### Steps to creating a good definition

1. Classify your term. What is it?

2. Differentiate your term. How does it differ from others in that class?

3. Test your definition by looking for a counterexample.

### Pair of vertical angles

angles formed by two intersecting lines; they share a common vertex but not a common side

### Pair of linear angles

two supplementary adjacent angles formed by 2 intersecting lines ; they share a vertex and a side

### Polygon

a closed figure in a plane, formed by connecting line segments endpoint to endpoint with each segment intersecting exactly two others. Each line segment is called a side of the polygon and each endpoint where the sides meet is called a vertex.

### Circle

the set of all points in a plane at a given distance (radius) from a given point (center) in the plane. Has an arc measure of 360 degrees.

### Radius

a segment from the center to a point on the edge of the circle. It's length is also called the radius.

### Diameter

a line segment containing the center, with its endpoints on the circle. The length of this segment is also called the diameter.

### Arc of a circle

two points on the circle and the continuous (unbroken) part of teh circle between the two points. The two points are called the endpoints of the arc.

### Semicircle

an arc of a circle whose endpoints are the endpoints of a diameter. It has an arc measure of 180 degrees.

### Central angle of a circle

the angle with its vertex at the center of the circle, and sides passing through the endpoints of the arc.

### Prism

A solid figure that has two congruent, parallel polygons as its bases. Its sides are parallelograms

### Sphere

a three-dimensional closed surface such that every point on the surface is equidistant from the center

### Isometric drawing

a 2-D drawing of an 3-D object, in which 3 sides of the object are shown from a corner view.

### Inductive reasoning

the process of observing data, recognizing patterns, and making generalizations about those patterns.

### Deductive reasoning

the process of showing that certain statements follow logically from agreed-upon assumptions and proven facts. Involves logical and orderly reasoning from accepted truths.

### Linear function

rules that generate a sequence with a constant difference. In the form f(n)=mx+b, where: f(n) is the value (y) or dependant variable; x is the term# or independant variable, m is the constant difference (coefficient, slope) and b is the y-intercept.

### Segment bisector

a line, rar, or segment in a plane that passes through the midpoint of a segment in a plane.

### Median of a triangle

the segment connecting the vertex of a triangle to the midpoint of its opposite side.

### Distance from a point to a line

is the length of the perpendicular segment from the point to the line.

### Altitude of a triangle

a perpendicular segment from a vertex to the opposite side or to a line containing the opposite side. It may be inside the triangle, outside the triangle or one of its sides. The length of the altitude is the height of the triangle. Every triangle has three.

### Concurrent

when three or more lines have a point in common. The point of intersection of segments, rays, planes or lines is called "the point of concurrency"

### Parts of a triangle

in a diagram, know which is: the vertex angle, the base angles, the legs and the base.

### Flickr Creative Commons Images

Some images used in this set are licensed under the Creative Commons through Flickr.com. Click to see the original works with their full license.

- “reflectional symmetry” image
- “rotational symmetry” image
- “bilateral symmetry” image
- “line” image
- “collinear” image
- “coplanar” image
- “line segment” image
- “congruent segments” image
- “midpoint” image
- “bisect” image
- “ray” image
- “angle” image
- “vertex” image
- “sides of an angle” image
- “measure of an angle” image
- “congruent angles” image
- “right angle” image
- “acute angle” image
- “obtuse angle” image
- “Pair of Complementary angles” image
- “Polygon” image
- “Diagonal of a polygon” image
- “Convex polygon” image
- “Right triangle” image
- “Square” image
- “Circle” image
- “Concentric circles” image
- “Semicircle” image
- “Pyramid” image