8.1.Vocabulary

Vertex - A vertex is a point where two or more edges meet. When we have more than one vertex, we call them vertices.

The vertices in this polygon are labeled A, B, C, D, and E. 

Clockwise - Clockwise means to turn in the same direction as the hands of a clock. The top turns to the right.

This diagram shows Figure A turned clockwise to make Figure B. 

Counterclockwise - Counterclockwise means to turn opposite of the way the hands of a clock turn. The top turns to the left.

This diagram shows Figure A turned counterclockwise to make Figure B.

Translation - A translation moves every point in a figure a given distance in a given direction.

This diagram shows a translation of Figure A to Figure B using the direction and distance given by the arrow.

Reflection - A reflection across a line moves every point on a figure to a point directly on the opposite side of the line. The new point is the same distance from the line as it was in the original figure. 

Rotation - A rotation moves every point on a figure around a center by a given angle in a specific direction. 

Image - An image is the result of translations, rotations, and reflections on an object. Every part of the original object moves in the same way to match up with a part of the image.

In this diagram, ABC triangle  has been translated up and to the right to make triangle DEF. Triangle DEF is the image of the original triangle ABC. 

Sequence of Transformations - A sequence of transformations is a set of translations, rotations, reflections, and dilations on a figure. The transformations are performed in a given order.

This diagram shows a sequence of transformations to move Figure A to Figure C.  First, A is translated to the right to make B. Next, B is reflected across line  to make C.

Coordinate Plane - The coordinate plane is a grid-like system for telling where points are located. For example. point R is located at (3,2)  on the coordinate plane, because it is three units to the right and two units up.

When describing ordered pairs, we 

always move along the x-axis first, and 

the y-axis second in order to plot the 

given point(s).

Corresponding - When part of an original figure matches up with part of a copy, we call them corresponding parts. These could be points, segments, angles, or distances.

For example, point B in the first triangle corresponds to point E in the second triangle. Segment AC corresponds to DF segment . 

Vertical Angles - Vertical angles are opposite angles that share the same vertex. They are formed by a pair of intersecting lines. Their angle measures are equal.

For example, angles AEC and  DEB are vertical angles. If angle AEC measures 1200, then angle DEB must also measure 1200.

Angles AED and BEC are another pair of vertical angles. 

Congruent - One figure is congruent to another if it can be moved with translations, rotations, and reflections to fit exactly over the other.

In the figure, Triangle A is congruent to Triangles B, C, and D. A translation takes Triangle A to Triangle B, a rotation takes Triangle B to Triangle C, and a reflection takes Triangle C to Triangle D.

Right Angle - A right angle is half of a straight angle. It measures 90 degrees.

Alternate Interior Angles - Alternate interior angles are created when two parallel lines are crossed by another line called a transversal. Alternate interior angles are inside the parallel lines and on opposite sides of the transversal.

This diagram shows two pairs of alternate interior angles. Angles a and d are one pair and angles b and c are another pair. 

Transversal - A transversal is a line that crosses parallel lines.

This diagram shows a transversal line k  intersecting parallel lines m and l. 

Straight Angle - A straight angle is an angle that forms a straight line. It measures 180 degrees.