### corresponding angles

Two angles that are formed by two lines and a transversal and occupy corresponding positions.

### alternate interior angles

Two angles that are formed by two lines and a transversal and lie between the two lines and on opposite sides of the transversal.

### alternate exterior angles

Two angles that are formed by two lines and a transversal and lie outside the two lines and on opposite sides of the transversal.

### consecutive interior angles

Two angles that are formed by two lines and a transversal and lie between the two lines and on the same side of the transversal. Also called same-side interior angles.

### slope

The slope m of a non-vertical line is the ratio of the vertical change (the rise) to horizontal change (the run) between any two points on the line.

### slope-intercept form

A linear equation written in the form y = mx + b where m is the slope and b is the y-intercept of the equation's graph.

### standard form of a linear equation

A linear equation written in the form Ax + By = C, where A, B, and C are real numbers and A and B are not both zero.

### Parallell Postulate

If there is a line and a point not on the line, then there is exactly one line through the point parallel to the given line.

### Perpendicular Postulate

If there is a line and a point not on the line, then there is exactly one line through the point perpendicular to the given line.

### Corresponding Angles Postulate

If two parallel lines are cut by a transversal, then the pairs of corresponding angles are congruent.

### Corresponding Angles Converse

If two lines are cut by a transversal so the corresponding angles are congruent, then the lines are parallel.

### Slopes of Parallell Lines

In a coordinate plane, two non vertical lines are parallel if and only if they have the same slope. Any two vertical lines are parallel.

### Slopes of Perpendicular Lines

In a coordinate plane, two non vertical lines are perpendicular if and only if the product of their slopes is -1. Horizontal lines are perpendicular to vertical lines.

### Alternate Interior Angles Theorem

If two parallel lines are cut by a transversal, then the pairs of alternate interior angles are congruent.

### Alternate Exterior Angles Theorem

If two parallel lines are cut by a transversal, then the pairs of alternate exterior angles are congruent.

### Consecutive Interior Angles Theorem

If two parallel lines are cut by a transversal, then the pairs of consecutive interior angles are supplementary.

### Alternative Interior Angles Converse

If two lines are cut by a transversal so the alternate interior angles are congruent, then the lines are parallel.

### Alternate Exterior Angles Converse

If two lines are cut by a transversal so the alternate exterior angles are congruent, then the lines are parallel.

### Consecutive Interior Angles Converse

If two lines are cut by a transversal so the consecutive interior angles are supplementary, then the lines are parallel.

### Transitive Property of Parallel Lines

If two lines are parallel to the same line, then they are parallel to each other.

### Perpendicular Transversal Theorem

If a transversal is perpendicular to one of two parallel lines, then it is perpendicular to the other.