# 1.1 Identify Points, Lines, and Planes

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1 1.1 Identify Points, Lines, and Planes Objective: Name and sketch geometric figures. Key Vocabulary Undefined terms - These words do not have formal definitions, but there is agreement aboutwhat they mean. Point - A point has no dimension. It is represented by a dot. Line - A line has one dimension. It is represented by a line with two arrowheads, but it extends without end. Through any two points, there is exactly one line. You can use any two points on a line to name it. Line AB (written as ) and points A and B are used here to define the terms below. Plane - A plane has two dimensions. It is represented by a shape that looks like a floor or a wall, but it extends without end. Through any three points not on the same line, there is exactly one plane. You can use three points that are not all on the same line to name a plane. Collinear points - Collinear points are points that lie on the same line. Coplanar points - Coplanar points are points that lie in the same plane. Defined terms - In geometry, terms that can be described using known words such as point or line are called defined terms. Line segment, Endpoints - The line segment AB, or segment AB, (written as ) consists of the endpoints A and B and all points on that are between A and B. Note that can also be named. Ray - The ray AB (written as ) consists of the endpoint A and all points on that lie on the same side of A as B. Note that and are different rays. Opposite rays - If point C lies on between A and B, then and are opposite rays. Intersection - The intersection of the figures is the set of points the figures have in common. The intersection of two The intersection of two different lines is a point. different planes is a line. EXAMPLE 1 Name points, lines, and planes a. Give two other names for and for plane Z. b. Name three points that are collinear. Name four points that are coplanar.

2 EXAMPLE 2 Name segments, rays, and opposite rays a. Give another name for. b. Name all rays with endpoint W. Which of these rays are opposite rays? Solution EX (1.1 cont.) EXAMPLE 3 Sketch intersections of lines and planes a. Sketch a plane and a line that is in the plane. b. Sketch a plane and a line that does not intersect the plane. c. Sketch a plane and a line that intersects the plane at a point. EXAMPLE 4 Sketch intersections of planes Sketch two planes that intersect in a line. Solution STEP 1 Draw a vertical plane. Shade the plane. STEP 2 Draw a second plane that is horizontal. Shade this plane a different color. Use dashed lines to show where one plane is hidden. STEP 3 Draw the line of intersection.

3 1.1 Cont.

4 2.4 Use Postulates and Diagrams Obj.: Use postulates involving points, lines, and planes. Key Vocabulary Line perpendicular to a plane - A line is a line perpendicular to a plane if and only if the line intersects the plane in a point and is perpendicular to every line in the plane that intersects it at that point. Postulate - In geometry, rules that are accepted without proof are called postulates or axioms. POSTULATES Point, Line, and Plane Postulates POSTULATE 5 - Through any two points there exists exactly one line. POSTULATE 6 - A line contains at least two points. POSTULATE 7 - If two lines intersect, then their intersection is exactly one point. POSTULATE 8 - Through any three noncollinear points there exists exactly one plane. POSTULATE 9 - A plane contains at least three noncollinear points. POSTULATE 10 - If two points lie in a plane, then the line containing them lies in the plane. POSTULATE 11 - If two planes intersect, then their intersection is a line. CONCEPT SUMMARY - Interpreting a Diagram When you interpret a diagram, you can only assume information about size or measure if it is marked. YOU CAN ASSUME YOU CANNOT ASSUME All points shown are coplanar. G, F, and E are collinear. AHB and BHD are a linear pair. BF and CE intersect. AHF and BHD are vertical angles. BF and CE do not intersect. A, H, J, and D are collinear. BHA CJA AD and BF intersect at H. AD BF or m AHB = 90⁰ EXAMPLE 1 Identify a postulate illustrated by a diagram State the postulate illustrated by the diagram. Solution

5 EXAMPLE 2 Identify postulates from a diagram Use the diagram to write examples of Postulates 9 and 11. (2.4 cont.) EXAMPLE 3 Use given information to sketch a diagram Sketch a diagram showing RS perpendicular to TV, intersecting at point X. EXAMPLE 4 Interpret a diagram in three dimensions

6 2.4 Cont.

7 1.2 Use Segments and Congruence Obj.: Use segment postulates to identify congruent segments. Key Vocabulary Postulate, axiom - In Geometry, a rule that is accepted without proof is called a postulate or axiom. Coordinate - The points on a line can be matched one to one with the real numbers. The real number that corresponds to a point is the coordinate of the point. Distance - The distance between points A and B, written as AB, is the absolute value of the difference of the coordinates of A and B. Between- When three points are collinear, you can say that one point is between the other two. Congruent segments - Line segments that have the same length are called congruent segments. POSTULATE 1 Ruler Postulate POSTULATE 2 Segment Addition If B is between A and C, then AB + BC = AC. If AB + BC = AC, then B is between A and C. Lengths are equal. AB = CD is equal to Segments are congruent. is congruent to EXAMPLE 1 Apply the Ruler Postulate Measure the length of CD to the nearest tenth of a centimeter. Solution EXAMPLE 2 Apply the Segment Addition Postulate MAPS The cities shown on the map lie approximately in a straight line. Use the given distances to find the distance from Lubbock, Texas, to St. Louis, Missouri. Solution Because Tulsa, Oklahoma, lies between Lubbock and St. Louis, you can apply the Segment Addition Postulate. LS = LT + TS = = 740 The distance from Lubbock to St. Louis is about 740 miles.

8 EXAMPLE 3 Find a length Use the diagram to find KL. Solution Use the Segment Addition Postulate to write an equation. Then solve the equation to find KL. (1.2 cont.) EXAMPLE 4 Compare segments for congruence Plot F(4, 5), G( 1, 5), H(3, 3), and J(3, 2) int a coordinate plane. Then determine whether FG and HJ are congruent.

9 1.3 Use Midpoint and Distance Formulas Obj.: Find lengths of segments in the coordinate plane. Key Vocabulary Midpoint - The midpoint of a segment is the point that divides the segment into two congruent segments. Segment bisector - A segment bisector is a point, ray, line, line segment, or plane the at intersects the segment at its midpoint. M is the midpoint of AB. CD is a segment bisector of AB.. So, AB AB and AM = MB. The Midpoint Formula KEY CONCEPT The coordinates of the midpoint of a segment are the averages of the x-coordinates and of the y-coordinates of the endpoints. If A(x₁, y₁) and B(x₂, y₂) are points in a coordinate plane, then the midpoint M of AB has coordinates x 1 x y1 y 2 2, 2 2 The Distance Formula KEY CONCEPT If A(x₁, y₁) and B(x₂, y₂) are points is a coordinate plane, then the distance between A and B is 2 AB = x x y y 1 So, AB AB and AM = MB. EXAMPLE 1 Find segment lengths Find RS. EXAMPLE 2 Use algebra with segment lengths ALGEBRA Point C is the midpoint of BD. Find the length of BC.

10 EXAMPLE 3 Use the Midpoint Formula a. FIND MIDPOINT The endpoints of PR are P( 2, 5) and R(4, 3). Find the coordinates of the midpoint M. (1.3 cont.) b. FIND ENDPOINT The midpoint of AC is M(3, 4). One endpoint is A(1, 6). Find the coordinates of endpoint C. The Distance Formula is based on the Pythagorean Theorem, which you will see again when you work with right triangles in Chapter 7. Distance Formula Pythagorean Theorem EXAMPLE 4 Use the Distance Formula What is the approximate length of TR, with endpoints T( 4, 3) and R(3, 2)?

11 1.3 Cont.

12 1.4 Measure and Classify Angles Obj.: Name, measure, and classify angles. Key Vocabulary Angle - An angle consists of two different rays with the same endpoint. Sides, vertex of an angle - The rays are the sides of the angle. The endpoint is the vertex of the angle. Measure of an angle - A protractor can be used to approximate the measure of an angle. An angle is measured in units called degrees (⁰). Words The measure of WXZ is 32⁰. Symbols m WXZ = 32⁰ Congruent angles - Two angles are congruent angles if they have the same measure. Angle bisector - An angle bisector is a ray that divides an angle into two angles that are congruent. POSTULATE 3 - Protractor Postulate Consider OB and a point A on one side of OB. The rays of the form OA can be matched one to one with the real numbers from 0 to 180. The measure of AOB is equal to the absolute value of the difference between the real numbers for OA and OB. CLASSIFYING ANGLES Angles can be classified as acute, right, obtuse, and straight, as shown below. the red square means a right angle POSTULATE 4 - Angle Addition Postulate (AAP) Words If P is in the interior of RST, then the measure of RST is equal to the sum of the measures of RSP and PST. Symbols If P is in the interior of RST, then m RST = m RSP + m PST. interior Angle measures are equal. Angles are congruent. the arcs show that the m A = m B A B angels are congruent equal to is congruent to

13 EXAMPLE 1 Name angles Name the three angles in the diagram. (1.4 cont.) EXAMPLE 2 Measure and classify angles Use the diagram to find the measure of the indicated angle. Then classify the angle. a. WSR b. TSW c. RST d. VST EXAMPLE 3 Find angle measures ALGEBRA Given that m GFJ = 155⁰, find m GFH and m HFJ. EXAMPLE 4 Identify congruent angles Identify all pairs of congruent angles in the diagram. If m P = 120⁰, what is m N? EXAMPLE 5 Double an angle measure In the diagram at the right, WY bisects XWZ, and m XWY = 29⁰. Find m XWZ

14 1.4 Cont.

15 2.6 Prove Statements about Segments and Angles Obj.: Write proofs using geometric theorems. Key Vocabulary Proof - A proof is a logical argument that shows a statement is true. There are several formats for proofs. Two-column proof - A two-column proof has numbered statements and corresponding reasons that show an argument in a logical order. Theorem - The reasons used in a proof can include definitions, properties, postulates, and theorems. A theorem is a statement that can be proven. THEOREMS Congruence of Segments Segment congruence is reflexive, symmetric, and transitive. Reflexive For any segment AB, AB AB. Symmetric If AB CD, then CD AB. Transitive If AB CD and CD EF, then AB EF. Congruence of Angles Angle congruence is reflexive, symmetric, and transitive. Reflexive For any angle A, A A. Symmetric If A B, then B A. Transitive If A B and B C, then A C. EXAMPLE 1 Write a two-column proof Use the diagram to prove m 1 = m 4. Given: m 2 = m 3, m AXD = m AXC Prove: m 1 = m 4 EXAMPLE 2 Name the property shown Name the property illustrated by the statement. If 5 3, then 3 5

16 EXAMPLE 3 Use properties of equality If you know that BD bisects ABC, prove that m ABC is two times m 1. Given: BD bisects ABC. Prove: m ABC = 2 m 1 (2.6 cont.) EXAMPLE 4 Solve a multi-step problem Interstate There are two exits between rest areas on a stretch of interstate. The Rice exit is halfway between rest area A and Mason exit. The distance between rest area B and Mason exit is the same as the distance between rest area A and the Rice exit. Prove that the Mason exit is halfway between the Rice exit and rest area B. CONCEPT SUMMARY - Writing a Two-Column Proof In a proof, you make one statement at a time, until you reach the conclusion. Because you make statements based on facts, you are using deductive reasoning. Usually the first statement-andreason pair you write is given information. Proof of the Symmetric Property of Angle Congruence GIVEN 1 2 PROVE 2 1 Copy or draw diagrams and label given information to help develop proofs. The number of Remember to give a reason 1 2 statements will vary for the last statement.

17 Definitions, postulates Theorems Statements based on facts that you know or on conclusions from deductive reasoning 2.6 Cont.

18 1.5 Describe Angle Pair Relationships Obj.: Use special angle relationships to find angle measure. Key Vocabulary Complementary angles - Two angles are complementary angles if the sum of their measures is 90⁰. Supplementary angles - Two angles are supplementary angles if the sum of their measures is 180⁰. Adjacent angles - Adjacent angles are two angles that share a common vertex and side, but have no common interior points. Linear pair - Two adjacent angles are a linear pair if their noncommon sides are opposite rays. Vertical angles - Two angles are vertical angles if their sides form two pairs of opposite rays. 1 and 2 are a linear pair. 3 and 6 are vertical angles. 4 and 5 are vertical angles. EXAMPLE 1 Identify complements and supplements In the figure, name a pair of complementary angles, a pair of supplementary angles, and a pair of adjacent angles. EXAMPLE 2 Find measures of a complement and a supplement a. Given that 1 is a complement of 2 and m 2 = 57⁰, find m 1. b. Given that 3 is a supplement of 4 and m 4 = 41⁰, find m 3.

19 EXAMPLE 3 Find angle measures SPORTS The basketball pole forms a pair of supplementary angles with the ground. Find m BCA and m DCA. (1.5 cont.) EXAMPLE 4 Identify angle pairs Identify all of the linear pairs and all of the vertical angles in the figure at the right. EXAMPLE 5 Find angle measures in a linear pair ALGEBRA Two angles form a linear pair. The measure of one angle is 4 times the measure of the other. Find the measure of each angle. CONCEPT SUMMARY Interpreting a Diagram There are some things you can conclude from a diagram, and some you cannot. For example, here are some things that you can conclude from the diagram at the right: All points shown are coplanar. Points A, B, and C are collinear, and B is between A and C. AC, BD, and BE intersect at point B. DBE and EBC are adjacent angles, and ABC is a straight angle. Point E lies in the interior of DBC. In the diagram above, you cannot conclude that AB BC, that DBE EBC, or that ABD is a right angle. This information must be indicated by marks, as shown at the right.

20 1.5 Cont.

21 2.7 Prove Angle Pair Relationships Obj.: Use properties of special pairs of angles. Key Vocabulary Complementary angles - Two angles whose measures have the sum 90. Supplementary angles - Two angles whose measures have the sum 180. Linear pair - Two adjacent angles whose noncommon sides are opposite rays. Vertical angles Two angles whose sides form two pairs of opposite rays. Right Angles Congruence Theorem All right angles are congruent. Abbreviation All Rt. s Congruent Supplements Theorem If two angles are supplementary to the same angle (or to congruent angles), then they are congruent. If 1 and 2 are supplementary and 3 and 2 are supplementary, then 1 3. Congruent Complements Theorem If two angles are complementary to the same angle (or to congruent angles), then they are congruent. If 4 and 5 are complementary and 6 and 5 are complementary, then 4 6. Supp. Th Comp. Th Linear Pair Postulate If two angles form a linear pair, then they are supplementary. 1 and 2 form a linear pair, so 1 and 2 are supplementary and m 1 +m 2 = 180⁰. Vertical Angles Congruence Theorem Vertical angles are congruent. 1 3, 2 4 EXAMPLE 1 Use right angle congruence Write a proof. GIVEN: JK KL, ML KL PROVE: K L

22 EXAMPLE 2 Use Congruent Supplements Theorem Write a proof. GIVEN: 1 and 2 are supplements. 1 and 4 are supplements. m 2 = 45⁰ PROVE: m 4 = 45⁰ (2.7 cont.) EXAMPLE 3 Use the Vertical Angles Congruence Theorem Prove vertical angles are congruent. GIVEN: 4 is a right angle. PROVE: 2 and 4 are supplementary. EXAMPLE 4 Find angle measures Write and solve an equation to find x. Use x to find the m FKG.

23 2.7 Cont.

24 1.6 Classify Polygons Obj.: Classify polygons. Key Vocabulary Polygon - In geometry, a figure that lies in a plane is called a plane figure. A polygon is a closed plane figure with the following properties: Side - 1. It is formed by three or more line segments called sides. 2. Each side intersects exactly two sides, one at each endpoint, so that no two sides with a common endpoint are collinear. Vertex - Each endpoint of a side is a vertex of the polygon. The plural of vertex is vertices. Convex - A polygon is convex if no line that contains a side of the polygon contains a point in the interior of the polygon. Concave - A polygon that is not convex is called nonconvex or concave. n-gon - The term n-gon, where n is the number of a polygon s sides, can also be used to name a polygon. For example, a polygon with 14 sides is a 14-gon. Equilateral - In an equilateral polygon, all sides are congruent. Equiangular - In an equiangular polygon, all angles in the interior of the polygon are congruent. Regular - A regular polygon is a convex polygon that is both equilateral and equiangular. regular pentagon A polygon can be named by listing the vertices in consecutive order. For example, ABCDE and CDEAB are both correct names for the polygon at the right. cave in convex polygon concave polygon CLASSIFYING POLYGONS A polygon is named by the number of its sides. # of sides Type of polygon # of sides Type of polygon 3 Triangle 8 Octagon 4 Quadrilateral 9 Nonagon 5 Pentagon 10 Decagon 6 Hexagon 12 Dodecagon 7 Heptagon n n-gon

25 EXAMPLE 1 Identify polygons Tell whether the figure is a polygon and whether it is convex or concave. (1.6 cont.) EXAMPLE 2 Classify polygons Classify the polygon by the number of sides. Tell whether the polygon is equilateral, equiangular, or regular. Explain your reasoning. EXAMPLE 3 Find side lengths + ALGEBRA A head of a bolt is shaped like a regular hexagon. The expressions shown represent side lengths of the hexagonal bolt. Find the length of a side.

26 1.6 Cont. (Write these on your paper)

27 2.1 Use Inductive Reasoning Obj.: Describe patterns and use inductive reasoning. Key Vocabulary Conjecture - A conjecture is an unproven statement that is based on observations. Inductive reasoning - You use inductive reasoning when you find a pattern in specific cases and then write a conjecture for the general case. Counterexample - A counterexample is a specific case for which the conjecture is false. You can show that a conjecture is false, however, by simply finding one counterexample. EXAMPLE 1 Describe a visual pattern Describe how to sketch the fourth figure in the pattern. Then sketch the fourth figure. EXAMPLE 2 Describe a number pattern Describe the pattern in the numbers 1, 4, 16, 64,... and write the next three numbers in the pattern. EXAMPLE 3 Make a conjecture Given five noncollinear points, make a conjecture about the number of ways to connect different pairs of the points.

28 EXAMPLE 4 Make and test a conjecture Numbers such as 1, 3, and 5 are called consecutive odd numbers. Make and test a conjecture about the sum of any three consecutive odd numbers. (2.1 cont.) EXAMPLE 5 Find a counterexample A student makes the following conjecture about the difference of two numbers. Find a counterexample to disprove the student s conjecture. Conjecture The difference of any two numbers is always smaller than the larger number. EXAMPLE 6 Real world application The scatter plot shows the average salary of players in the National Football League (NFL) since Make a conjecture based on the graph.

29 2.1 Cont.

30 2.3 Apply Deductive Reasoning Obj.: Use deductive reasoning to form a logical argument. Key Vocabulary Deductive reasoning - Deductive reasoning uses facts, definitions, accepted properties, and the laws of logic to form a logical argument. **** This is different from inductive reasoning, which uses specific examples and patterns to form a conjecture.**** Laws of Logic KEY CONCEPT Law of Detachment If the hypothesis of a true conditional statement is true, then the conclusion is also true. Law of Syllogism If hypothesis p, then conclusion q. If these statements are true, If hypothesis q, then conclusion r. If hypothesis p, then conclusion r. then this statement is true. EXAMPLE 1 Use the Law of Detachment Use the Law of Detachment to make a valid conclusion in the true situation. a. If two angles have the same measure, then they are congruent. You know that m A = m B. b. Jesse goes to the gym every weekday. Today is Monday. EXAMPLE 2 Use the Law of Syllogism (2.3 cont.) If possible, use the Law of Syllogism to write a new conditional statement that follows from the pair of true statements. a. If Ron eats lunch today, then he will eat a sandwich. If Ron eats a sandwich, then he will drink a glass of milk.

31 b. If x² > 36, then x² > 30. If x > 6, then x² > 36. c. If a triangle is equilateral, then all of its sides are congruent. If a triangle is equilateral, then all angles in the interior of the triangle are congruent. EXAMPLE 3 Use inductive and deductive reasoning What conclusion can you make about the sum of an odd integer and an odd integer? EXAMPLE 4 Reasoning from a graph Tell whether the statement is the result of inductive reasoning or deductive reasoning. Explain your choice. a. The runner s average speed decreases as time spent running increases. b. The runner s average speed is slower when running for 40 minutes than when running for 10 minutes.

32 2.3 Cont.

33 2.2 Analyze Conditional Statements Obj.: Write definitions as conditional statements. Key Vocabulary Conditional statement - A conditional statement is a logical statement that has two parts, a hypothesis and a conclusion. Converse - To write the converse of a conditional statement, exchange the hypothesis and conclusion. Inverse - To write the inverse of a conditional statement, negate (not) both the hypothesis and the conclusion. Contrapositive - To write the contrapositive, first write the converse and then negate both the hypothesis and the conclusion. If-then form, Hypothesis, Conclusion - When a conditional statement is written in if-then form, the if part contains the hypothesis and the then part contains the conclusion. Here is an example: hypothesis conclusion Negation - The negation of a statement is the opposite of the original statement. Equivalent statements - When two statements are both true or both false, they are called equivalent statements. Perpendicular lines - If two lines intersect to form a right angle, then they are perpendicular lines. You can write line l is perpendicular to line m as l m. KEY CONCEPT l m. Biconditional statement A biconditional statement is a statement that contains the converse and the phrase if and only if. EXAMPLE 1 Rewrite a statement in if-then form Rewrite the conditional statement in if-then form. All vertebrates have a backbone.

34 EXAMPLE 2 Write four related conditional statements Write the if-then form, the converse, the inverse, and the contrapositive of the conditional statement Olympians are athletes. Decide whether each statement is true or false. If-then form (2.2 cont.) Converse Inverse Contrapositive EXAMPLE 3 Use definitions Decide whether each statement about the diagram is true. Explain your answer using the definitions you have learned. a. AC BD b. AED and BEC are a linear pair. EXAMPLE 4 Write a biconditional Write the definition of parallel lines as a biconditional. Definition: If two lines lie in the same plane and do not intersect, then they are parallel.

35 2.2 Cont.

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