# Pre-algebra chapter 9 vocab

## 20 terms

Adjacent angles are two angles that share a vertex and a side but no points in their interiors.

### alternate interior angles

Alternate interior angles are angles between two lines and on opposite sides of a transversal.

### angle bisector

An angle bisector is a ray that divides a given angle into two congruent angles, each half the size of the given angle.

### complementary

Complementary angles are two angles whose measures add to 90°.

### congruent angles

Congruent angles are angles that have the same measure.

### congruent figures

Congruent figures are figures that have the same size and shape. Congruent polygons have congruent corresponding sides and congruent corresponding angles. The symbol means "is congruent to."

### corresponding angles

Corresponding angles are pairs of nonadjacent angles that lie on the same side of a transversal of two lines and in corresponding positions.

### parallel

Parallel lines are lines that lie in the same plane and do not intersect. The symbol || means "is parallel to."

### perpendicular bisector

A perpendicular bisector is a line, segment, or ray that is perpendicular to a segment at its midpoint.

### perpendicular lines

Perpendicular lines are lines that intersect to form right angles.

### polygon

A polygon is a closed plane figure with at least three sides.

### reflection

A reflection is a transformation that flips a figure over a line of reflection.

### regular polygon

A regular polygon is a polygon with all its sides congruent and all its angles congruent.

### rotation

A rotation is a transformation that turns a figure about a fixed point, called the center of rotation. The angle measure of the rotation is the angle of rotation.

### segment

A segment is part of a line. It has two endpoints.

### segment bisector

A segment bisector is a line, segment, or ray that separates a segment into two congruent segments.

### supplementary

Supplementary angles are two angles whose measures add to 180°.

### symmetry

A figure has reflectional symmetry when one half of the figure is a mirror image of the other half. The line of reflection is also called the line of symmetry.

### translation

A translation is a transformation that moves points the same distance and in the same direction.

### vertical angles

Vertical angles are angles formed by two intersecting lines, and are opposite each other. Vertical angles are congruent.