Parallel lines 
Two lines that lie in the same plane and do not intersect. 
Perpendicular lines 
Two lines that intersect to form a right angle. 
Skew lines 
Two lines that do not lie in the same plane and do not intersect 
Parallel planes 
Two planes that do not intersect 
Transversal 
A line that intersects two or more coplanar lines at different points 
Corresponding angles 
Two angles formed by two lines and a transversal, and occupy corresponding positions 
Alternate interior angles 
Two angles formed by two lines and a transversal and lie between the two lines on the opposite sides of the transversal 
Alternate exterior angles 
Two angles formed by two lines and a transversal and lie outside the two lines on the opposite sides of the transversal 
Sameside interior angles 
Two angles formed by two lines and a transversal and lie between the two lines on the same side of the transversal 
Converse 
The statement formed by switching the hypothesis and the conclusion in an ifthen statement 
Hypothesis 
The "if" part of an ifthen statement 
Conclusion 
The "then" part of an ifthen statement 
All right angles are ____________ 
congruent 
If two lines are perpendicular, then they intersect to form four _______ ________. 
right angles 
If two lines intersect to form adjacent congruent angles, then the lines are _____________________. 
perpendicular 
If two sides of adjacent acute angles are perpendicular, then the angles are ___________________. 
complementary 
If two parallel lines are cut by a transversal, then ______________ interior angles are congruent. 
alternate 
If two parallel lines are cut by a transversal, then _____________ exterior angles are congruent. 
alternate 
If two parallel lines are cut by a transversal, then _______________ interior angles are supplementary. 
sameside 
If two lines are cut by a transversal so that alternate interior angles are congruent, then the lines are ___________________. 
parallel 
If two lines are cut by a transversal so that alternate exterior angles are congruent, then the lines are _____________________. 
parallel 
If two lines are cut by a transversal so that sameside interior angles are _________________, then the lines are parallel. 
supplementary 
If two lines are parallel to the same line, then they are _________ to each other. 
parallel 
In a plane, if two lines are perpendicular to the same line, then they are ___________ to each other. 
parallel 
Midpoint 
The point on a segment that divides the segment into two equal parts. 
Segment bisector 
Something that intersects a segment at it’s midpoint. 
Bisect 
To divide into two congruent parts. 
Angle bisector 
A ray that divides an angle into two equal angles. 
Complementary angles 
Two angles whose measures have a sum of 90 degrees. 
Supplementary angles 
Two angles whose measure has a sum of 180 degrees. 
Adjacent angles 
Two angles with a common vertex and side but no common interior points. 
Theorem 
A true statement that follows from other true statements. 
Vertical angles 
Two nonadjacent angles formed by two intersecting lines. 
Linear pair 
Two adjacent angles whose noncommon sides are on the same line (supplementary). 
Ifthen statements 
A statement with a hypothesis (if) and conclusion (then). 
Deductive reasoning 
Using facts, definitions, accepted properties to make a logical argument. 
Congruent complements theorem 
If two angles are complementary to the same angle, then they are congruent. 
Congruent supplements theorem 
If two angles are supplements to the same angle, then they are congruent. 
Vertical angles theorem 
Vertical angles are congruent. 
Reflexive Property 
A=A 
Symmetric Property 
If A=B, then B=A 
Transitive Property 

2.1 Congruent Complements Theorem 
If two angles are complements to the same angle, then they are congruent. 
2.2 Congruent Supplements Theorem 
If two angles are supplements to the same angle, then they are congruent. 
2.3 Vertical Angles Theorem 
When two lines intersect, they form two sets of vertical angels. Vertical angles are congruent. <a=<b 
angle 
a geometric figure formed by two rays with a common end point 
protractor 
a tool used to measure angles 
acute angle 
an angle that is greater than 0 degrees and less than 90 degrees 
right angle 
an angle that equals 90 degrees 
obtuse angle 
an angle that is greater than 90 degrees and less than 180 degrees 
straight angle 
an angle equal to 180 
adjacent angle 
two angles that have a common vertex and a common ray 
complementary angles 
a pair of angles whose measures have the sum of 90 degrees 
supplementary angles 
a pair of angles whose measures have the sum of 180 degrees 
congruent angles 
angles that have the same measure 
vertical angles 
angles formed by intersecting lines 
angle bisector 
a ray that divides an angle into two congruent angles 
inductive reasoning 
reasoning that a statement or rule is true because specific cases are true 
law of detachment 
says 1. if p then q 2. p so we can get a third statement 3. q 
law of syllogism 
says 1. if p then q 2. if q then r so we get a third statement 3. if p then r 
Geometry
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