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Acute Angle. An angle whose measure is less than 90°. Adjacent Angles. Two angles with a common vertex and a common side. Alternate Exterior Angles. 2 and 8 1 and 7.
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Acute Angle An angle whose measure is less than 90°
Adjacent Angles Two angles with a common vertex and a common side.
Alternate Exterior Angles 2 and 8 1 and 7 Two non-adjacent angles that lie on the opposite sides of a transversal outside two lines that the transversal intersects. If the lines are parallel, then the angles are congruent.
Alternate Interior Angles 3 and 6 4 and 5 Two non-adjacent angles that lie on the opposite sides of a transversal between two lines that the transversal intersects. If the lines are parallel, then the angles are congruent.
Angle X 3 V Z Formed by 2 rays (sides) with the same endpoint (vertex).
Angle Addition Postulate If T is in the interior of ∠QRS, then m∠QRT+ m∠TRS= m∠QRS.
Angle Bisector B A D C A ray that divides an angle into two congruent angles.
Auxiliary Line A line (or ray or segment) added to a diagram to help in a proof or in determining the solution to a problem. DE is an auxiliary line.
Biconditional Two statements connected by the words “if and only if.”
Collinear Points that are on the same line. B C D A E A, B, C, and D are collinear points. A, B, C, D, and E are non-collinear points.
Complementary Two angles whose measures have a sum of 90.
Compound Statement A statement formed when two or more simple statements are connected as either a conditional (if-then), a biconditional (if and only if), a conjunction (and), or a disjunction (or).
Conclusion The “then” statement in an if-then statement.
Conditional Statement A statement that tells if one thing happens another will follow. Example: “If a polygon has three sides then it is a triangle.”
Congruent Exactly equal in size and shape. Congruent segments have the same length. Congruent angles have the same measure.
Congruent Angles Angles that have the same measure. X W
Congruent Segments J K L M Segments that have the same length.
Conjecture An educated guess, opinion, hypothesis.
Conjunction Two statements joined by the word and, represented by the symbol ^.
Contrapositive A version of a conditional statement formed by interchanging and negating both the hypothesis and conclusion of the statement.
Converse A version of a conditional statement formed by interchanging the hypothesis and conclusion of the statement.
Coplanar Lines Lines that are in the same plane.
Coplanar Points Points that are in the same plane. F A C A, B, C, D, and E are coplanar points. A, B, C, D, E, and F are non-coplanar points. D B E
Corresponding Angles 1 and 5 2 and 4 3 and 8 4 and 7 Two non-adjacent angles that lie on the same side of a transversal, in “corresponding” positions with respect to the two lines that the transversal intersects. If the lines are parallel, then the angles are congruent.
Counterexample An example that shows that a conjecture is not always true.
Deductive Reasoning The use of facts, definitions, rules and/or properties to prove that a conjecture is true.
Disjunction The symbol v represents a disjunction, you read it as “or.”
Distance Formula The distance between can be found using the formula
Endpoint A point at one end of a segment or the starting point of a ray.
Hypothesis The “if” clause in an if-then statement.
Inductive Reasoning The process of observing data, recognizing patterns, and making a generalization.
Inverse A version of a conditional statement formed by negating both the hypothesis and conclusion of the statement.
Line A set of points that extends in 2 directions without end. m A B Line m or line AB or AB
Line Segment Part of a line consisting of two endpoints and all points between them. N M Segment MN or Segment NM or MN or NM
Linear Pair A pair of adjacent angles whose noncommon side are opposite rays.
Logically Equivalent When two statements have the same exact truth values.
Midpoint A B C A point that divides a segment into two congruent segments.
Midpoint Formula The midpoint of a segement with endpoints can be found using the formula
Negation of p The symbol ~p is the negation of p and can be read as “not p.”
Obtuse Angle An angle whose measure is greater than 90° but less than 180°.
Opposite Rays F H D Two collinear rays with the same endpoint. They always form a line. HF and HD are opposite rays.
Parallel Lines a c Coplanar lines that do not intersect. a//c
Parallel Planes W M Planes that do not intersect.
Perpendicular Lines A C B 2 lines intersect to form right angles.
Perpendicular Planes B D Planes intersect to form right angles.
Plane A flat surface that extends in all directions without end. It has no thickness. W A B C Plane W or Plane ABC
Point A location in space •A
Postulate A statement that is accepted without proof.
Proof An argument that transforms a conjecture to a theorem through the application of logical reasoning or deductive reasoning.
Pythagorean Theorem For sides a, b, and c in a right triangle, a2 + b2 = c2.