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### vertical angles

When angles are across from one another in an X pattern,Vertical angles are congruent

### perpendicular lines

If two lines intersect, and one of the angles is 90°, then the lines are perpendicular.

### perpendicular bisector

If a line or a segment is perpendicular to another segment at its midpoint,The distances of any point on the perpendicular bisector from both endpoints of the line being bisected are the same. If any point on the perpendicular bisector is connected to the endpoints of the segment being bisected, the angles formed at the endpoints are congruent.

### skew lines

Two lines that are in the same plane are called coplanar lines; otherwise they are referred to as

### concurrent lines

If a set of two or more lines intersect in only one point, concurrent lines are another form of intersecting lines

### perpendicular lines theorem

If two lines are perpendicular, then they form congruent adjacent angles

If two lines form congruent adjacent angles, then the lines are perpendicular.

If the exterior sides of two adjacent acute angles are perpendicular, then the angles are complimentary

### the properties of a perpendicular bisector

The distances of any point on the perpendicular bisector from both endpoints of the line being bisected are the same.

If any point on the perpendicular bisector is connected to the endpoints of the segment being bisected, the angles formed at the endpoints are congruent.

### congruent angles when parallel lines are cut by a transversal

Alternate Interior Angles are located between the parallel lines and on opposite sides of the transversal.