Geometry Foundations: Segment & Angle Measurement, Basic Constructions, Midpoint & Distance
Lesson 1-1: Measuring Segments and Angles
Learning Goals and Standards
Learning Objective: Use properties of segments and angles to find their measures.
Texas Essential Knowledge and Skills (TEKS):
: Distinguish between undefined terms, definitions, postulates, conjectures, and theorems.
: Determine coordinates of a point that is a given fractional distance less than one from one end of a line segment to the other.
Mathematical Process Standards: , , , , , .
Essential Question: How are the properties of segments and angles used to determine their measures?
Core Vocabulary: collinear points, line, plane, point, postulate.
Undefined Terms
Undefined terms are terms whose meanings are accepted without formal definition. They serve as the foundational building blocks of geometry.
Point:
Description: A point is a location and has no size.
Diagram: Represented by a dot labelled with point .
Notation: A single capital letter, such as .
Line:
Description: A line consists of infinitely many points on a straight path that extends in two opposite directions with no end and no thickness.
Diagram: A straight path with arrowheads on both ends containing points and , or designated by line .
Notation: A single lowercase letter like line , or any two points on the line written beneath a double-sided arrow symbol: .
Plane:
Description: A plane consists of infinitely many points and lines on a flat surface that extends without end and has no thickness.
Diagram: A slanted four-sided flat surface designated as plane or containing non-collinear points , , and Z$.\n - Notation: A single capital letter such as plane MXYZ$.
Defined Terms
Defined terms are terms constructed using previously defined or known geometric terms.
Segment (Line Segment):
Description: Part of a line consisting of two endpoints and all points between them.
Notation: Named by its two endpoints with a solid bar over them, such as . Length is written without the bar: AB$.\n - Ray:\n - Description: Part of a line consisting of one endpoint and all the points of the line on one side of the endpoint.\n - Notation: Named using its endpoint first followed by any other point on the ray with a single-direction arrow: \overrightarrow{MN}.\n - Opposite Rays:\n - Description: Rays with the exact same endpoint that lie on the same line extending in opposite directions.\n - Example: Given points STU\overrightarrow{TS}\overrightarrow{TU}.\n - Angle:\n - Description: Formed by two rays with the same endpoint. Each ray is a side of the angle, and the common endpoint is the vertex of the angle.\n - Diagram: Vertex Q\overrightarrow{QP}\overrightarrow{QR}2$.
Notation: Named by its vertex , three points with the vertex listed in the middle , or an interior number \angle 2$.\n\n- Measuring Segment Lengths\n - Definition of Segment Length: The length of a segment is a positive real number representing the distance between its endpoints.\n - Postulate 1-1 (Ruler Postulate):\n - Every point on a line can be paired with a unique real number called the coordinate of the point.\n - The distance between two points is the absolute value of the difference between their coordinates.\n - Example: Point X3\,cmY7\,cmXY = |7 - 3| = 4\,cm.\n - Example 1 Calculations:\n - On a number line with points A(-3)B(-1)C(1)D(4):\n - Length CD = |4 - 1| = 3\n - Length AC = |1 - (-3)| = |1 + 3| = 4\n - Example 2 Calculations:\n - Coordinates on a centimeter scale: K = 12L = 16M = 27.\n - KM = |27 - 12| = 15KM = |12 - 27| = 15\n - LM = |27 - 16| = 11LM = |16 - 27| = 11\n - KL = |16 - 12| = 4KL = |12 - 16| = 4\n - Key Principle: Distance is strictly positive; always evaluate distance as the absolute value of the coordinate difference.\n - Notation Distinction:\n - \overline{AB}AB).\n - AB\overline{AB}).\n\n- Segment Addition\n - Collinear Points: Points that lie on the same line.\n - Postulate 1-2 (Segment Addition Postulate):\n - If points ABCBACAB + BC = AC$.
Example 3 (Solving Algebraic Segments):
Given collinear points , , and with , , and .
Step 1: Solve for using :
Step 2: Calculate total length using the Segment Addition Postulate:
Common Error Warning: Do not mistake the value of for the final answer when the problem asks for a segment length.
Try It 3 Questions:
Points , , and are collinear with , , and JL = 25$.\n - Part a: Find n:\n 3n + (5n - 7) = 25 \implies 8n - 7 = 25 \implies 8n = 32 \implies n = 4\n - Part b: Find JKKL:\n JK = 3(4) = 12\n KL = 5(4) - 7 = 20 - 7 = 13\n\n- Angle Measurement and Protractor Use\n - Protractor Postulate (Example 4):\n - Real numbers are assigned to rays extending from a central vertex.\n - Given ray \overrightarrow{EA}0^\circ on the protractor scale:\n - Ray \overrightarrow{EB}47^\circ.\n - Ray \overrightarrow{EC}105^\circ.\n - The measure of \angle BECm\angle BEC) is evaluated as the absolute difference between ray values:\n m\angle BEC = |105^\circ - 47^\circ| = 58^\circ\n Alternatively: m\angle BEC = m\angle AEC - m\angle AEB = 105^\circ - 47^\circ = 58^\circ\n - Postulate 1-4 (Angle Addition Postulate):\n - If point D\angle ABCm\angle ABD + m\angle DBC = m\angle ABC$.
Lesson 1-1 Practice Exercises and Solutions
Number Line Calculations (, , ):
Segment
Segment
Collinear Points with between and :
Given and :
Angle Addition Calculations:
Given and :
Additional Practice Set:
Number Line Points (, , , ):
Collinear Points with , , :
Collinear Points :
If , , and :
If : If , then
Error Analysis (Luis Angle Calculation):
Luis incorrectly stated that . His error was reading the incorrect scale on the protractor (mixing the inner scale reading with the outer scale reading rather than taking the absolute difference along a single consistent scale).
Newscast Camera Application:
Three cameras setup: Center camera faces anchor desk. Two side cameras angled away from center camera. Each camera has a field of view.
The outer boundary of each side camera extends to the left and right of center.
Total span covered by all three cameras = .
Lesson 1-2: Basic Constructions
Objectives and Standards
Learning Objective: Use a straightedge and compass to construct basic figures.
Core Vocabulary: angle bisector, construction.
TEKS : Construct congruent segments, congruent angles, a segment bisector, an angle bisector, perpendicular lines, the perpendicular bisector of a line segment, and a line parallel to a given line through a point not on a line using a compass and a straightedge.
Mathematical Process Standards: , , , , .
Essential Question: How are a straightedge and compass used to make basic constructions?
Geometric Congruence
Congruent Segments: Segments that have identical length.
Statement:
Visual Representation: Indicated by matching tick marks across segments.
Congruent Angles: Angles that have identical measure.
Statement:
Visual Representation: Indicated by matching arc marks within angles.
Properties of Congruence:
Reflexive Property of Congruence:
Symmetric Property of Congruence:
Transitive Property of Congruence:
Congruence Examples
Example 1 Part A:
Given , , and . Find .
Apply Angle Addition Postulate:
Example 1 Part B:
Find length given tick mark congruences: () and ().
Apply Segment Addition Postulate:
Try It 1 Questions:
Part a: Given , , and . If , solve for using angle relationships.
Part b: Given , , and perimeter , evaluate length .
Construction Rules and Definitions
Construction: A geometric figure drawn using strictly an unmarked straightedge and a compass.
Straightedge: A tool used solely to draw straight lines, rays, or line segments (not for measuring lengths).
Compass: A tool used to draw arcs and circles of defined radii, and to copy segment lengths.
Step-by-Step Construction Procedures
Copying a Line Segment (Copying to form ):
Step 1: Use a straightedge to draw line . Mark point on line \ell$.\n - Step 2: Place the compass point at AAB$.
Step 3: Keeping the exact compass setting, place the point at and draw an arc intersecting line . Label the intersection point N$.\n - Result: Constructed segment \overline{MN} \cong \overline{AB}.\n - Copying an Angle (Copying \angle A\angle YXZ):\n - Step 1: Mark point XX$.
Step 2: Place the compass point at . Draw an arc intersecting both rays of . Label intersection points and C$.\n - Step 3: Without changing the compass setting, place the point at XY$.
Step 4: Place compass point at , and open the compass setting to distance BC$.\n - Step 5: Without changing the setting, place the compass point at YZ\overrightarrow{XZ}$.
Result: Constructed angle \angle YXZ \cong \angle A$.\n - Constructing an Angle Bisector (Bisecting \angle A\overrightarrow{AD}):\n - Definition: An angle bisector is a ray that divides an angle into two congruent adjacent angles.\n - Step 1: Place compass point at A\angle ABC$.
Step 2: Place compass point at and draw an arc in the interior of . Keeping the same compass setting (must be greater than half distance ), place compass point at and draw an arc intersecting the arc from B$.\n - Step 3: Label the arc intersection point D\overrightarrow{AD}$.
Result: Ray is the angle bisector of \angle A$.\n\n- Concept Summary and Reasoning Questions\n - Constructing vs Visual Appearance: Visual assessment ("looks the same") relies on optical perception and can be inaccurate. Constructing a figure guarantees geometric equivalence (\cong) backed by mathematical postulates.\n - Practice Problem 9: Given m\angle LMN = 116^\circm\angle JKM = 122^\circm\angle JNM = 103^\circm\angle NKM.\n\n# Lesson 1-3: Midpoint and Distance\n\n- Objectives and Standards\n - Learning Objective: Use the midpoint and distance formulas to solve coordinate plane problems.\n - Core Vocabulary: midpoint.\n - TEKS G.2A: Determine the coordinates of a point that is a given fractional distance less than one from one end of a line segment to the other in one- and two-dimensional coordinate systems, including finding the midpoint.\n - Mathematical Process Standards: G.1AG.1BG.1CG.1DG.1FG.1G$.
Essential Question: How are the midpoint and length of a segment on the coordinate plane determined?
Midpoint Formula and Derivation
Definition of Midpoint: The point that divides a line segment into two congruent segments.
Derivation:
The midpoint coordinates are the average of the -coordinates and the average of the -coordinates of segment endpoints and .
Midpoint Formula:
Example 2 Calculation:
Find the midpoint of with endpoints and :
Common Error Warning: Midpoint computation represents an average; add the coordinate values before dividing by .
Try It 2 Calculations:
Part a: Midpoint of and :
Part b: Midpoint of and :
Partitioning a Line Segment
Concept: Finding coordinates for a point partitioning line segment in a given ratio .
Ratio Conversion Rule: Convert part-to-part ratio to part-to-whole fraction .
Example 3 Step-by-Step Procedure:
Task: Partition in ratio from to .
Step 1: Calculate fractional distance from to :
Step 2: Compute of horizontal and vertical changes:
Step 3: Add changes to coordinates of starting point :
Try It 3 Tasks:
Part a: Find coordinates of point partitioning in ratio (uses fraction ).
Part b: Find coordinates of point located of the way from to A$.\n\n- Distance Formula and Concept Summary\n - Distance Formula:\n - Derived from Pythagorean Theorem for distance dP(x_1, y_1)Q(x_2, y_2):\n d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\n - Summary Example:\n - Endpoints P(-3, 4)Q(1, 7).\n - Midpoint:\n M = \left( \frac{-3 + 1}{2}, \frac{4 + 7}{2} \right) = \left( \frac{-2}{2}, \frac{11}{2} \right) = (-1, 5.5)\n - Distance:\n d = \sqrt{(1 - (-3))^2 + (7 - 4)^2} = \sqrt{(4)^2 + (3)^2} = \sqrt{16 + 9} = \sqrt{25} = 5\n\n- Lesson 1-3 Practice Exercises and Solutions\n - Midpoint Formula Definition:\n M = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)\n - Midpoint Computations:\n - A(-4, 6)B(10, -10)M = \left( \frac{-4+10}{2}, \frac{6+(-10)}{2} \right) = (3, -2)\n - C(-3, -8)D(-6.5, -4.5)M = \left( \frac{-3+(-6.5)}{2}, \frac{-8+(-4.5)}{2} \right) = (-4.75, -6.25)\n - E(3, 7)F(-8, -10)M = \left( \frac{3+(-8)}{2}, \frac{7+(-10)}{2} \right) = (-2.5, -1.5)\n - G(-6, -13)H(-6.4, -3.8)M = \left( \frac{-6+(-6.4)}{2}, \frac{-13+(-3.8)}{2} \right) = (-6.2, -8.4)\n - Partitioning Exercises on Segment \overline{CD}:\n - Ratio 1:2\frac{1}{1+2} = \frac{1}{3}CD$.
Ratio uses fraction of length from to D$.\n - Point \frac{2}{3}CD$.
Point of the way from to C$.\n - Distance Formula Definition:\n d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\n - Distance Computations:\n - A(6, 8)B(-1, 8)d = \sqrt{(-1-6)^2 + (8-8)^2} = \sqrt{(-7)^2 + 0} = 7\n - C(5, -6)D(5, 6)d = \sqrt{(5-5)^2 + (6-(-6))^2} = \sqrt{0 + 12^2} = 12\n - E(-2, 0)F(11, 0)d = \sqrt{(11-(-2))^2 + (0-0)^2} = \sqrt{13^2} = 13\n - Q(1, -5)T(9, 1)d = \sqrt{(9-1)^2 + (1-(-5))^2} = \sqrt{8^2 + 6^2} = \sqrt{64 + 36} = \sqrt{100} = 10\n - Segment Midpoint Algebraic Relation:\n - If M\overline{ST}STMT is:\n ST = 2 \cdot MT \quad \text{or} \quad MT = \frac{1}{2} ST\n - Coordinate Grid Bedroom Application:\n - Axes represent bedroom walls with one corner at origin (0,0).\n - Farthest bed corner evaluated at point (x, y) on coordinate plane.\n - Distance formula from origin: d = \sqrt{x^2 + y^2}$$.