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### Transitive Property of Parallel Lines

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

### Corresponding Angles Converse

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

### Alternate 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

### Slopes of Parallel lines

two nonvertical lines are parallel if and only if they have the same slope; any two vertical lines are parallel

### Slopes of perpendicular lines

two nonvertical lines are perpendicular if and only if the product of their slopes is -1. Horizontal lines are perpendicular to vertical lines.

### ...

If two lines intersect to form a linear pair of congruent angles, then the lines are perpendicular

### Perpendicular Transversal Theorem

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