Back To Course

Geometry for Kids6 chapters | 45 lessons

{{courseNav.course.topics.length}} chapters | {{courseNav.course.mDynamicIntFields.lessonCount}} lessons | {{course.flashcardSetCount}} flashcard set{{course.flashcardSetCoun > 1 ? 's' : ''}}

Instructor:
*Maria Airth*

Maria has a Doctorate of Education and over 20 years of experience teaching psychology and math related courses at the university level.

Boundary lines in math can relate to shapes or areas on an inequality graph. This lesson reviews the definition of boundary lines and gives examples of boundary lines for both shapes and inequality graphs.

Let's pretend you just got a new dog. You have a big yard, but no fence. You want to teach the dog how to stay in your yard and not run out in the street or into your neighbor's property. How do you do that? You would probably put the dog on a leash and walk him around the edge of the property. Every day, you would walk the dog around the edge of the property multiple times teaching him how far he is allowed to go.

**Boundary lines** in math are the same, they identify the outer edge (or outline) of a shape or area. This could be a geometric shape or an inequality graph. Each of these mathematical concepts includes a boundary line. Let's look at each in turn to get a better understanding of boundary lines and how they work.

When you did boundary training with your dog, you walked around the edge of your property line. If you were to look down at your property from a bird's eye view, you would see a geometric shape. Many properties are rectangular, but not all are. No matter the shape of your property, the boundary line of your property will create a geometric shape.

In math, we use the term **perimeter** to indicate the distance around the outer edge of a shape. In essence, when you do boundary training with your dog, you are walking the perimeter of your property. To find the perimeter (boundary line) of a shape, just add up the length of all the sides.

Perimeter = sum of sides

Ben's rectangular-shaped yard is 500ft across and 700ft deep. What is the measure of the boundary line for this yard?

Solution: Remembering that boundary line and perimeter are the same thing, we find the perimeter by adding up all the sides. P = 500 + 500 + 700 + 700 = 2400 ft

{Hint: Remember that a rectangle has four sides and opposite sides are equal; that's why we have two 500's and two 700's.}

What is the perimeter of this shape?

Solution: P = sum of sides = 4 + 5 + 3 = 12 in

Notice that the black line is the boundary line, or perimeter, of this yellow triangle.

When you graph an equation, you get a line. Right? Yes, if it is a true equation with an equal sign the graph will result in a line of some sort. For example, the equation *y* = *x* will be a straight line stretching from the bottom right to the top left corners of the graph, like this:

But, when you have an **inequality** the two sides of the mathematical sentence are not always the same value and the graph often ends up looking like a line with a shaded area. The graph of the line, as if it is an equation, is the boundary line for the inequality.

Look at this graph:

The line *y* = *x* + 1 is the boundary line and the solution for the inequality is anything under the line. Notice that the line is actually dotted, that means that points on the line itself are not actually included in the graph. This is because the mathematical sentence tells us that the solution is less than *x* + 1. So, the **boundary line in an inequality** shows the line past which solutions do not appear.

Take a look at this graph:

Again, the boundary line is *y* = *x* + 1, but this time, the line is solid meaning that the points on the line itself are included in the solution. This is because the inequality includes a symbol that means greater than or equal to, instead of just greater than. Still, the solution points do not cross the boundary line and because the solution (inequality direction) is greater than, the shaded part is above the line.

In this lesson, we saw that a **boundary line** is the outer edge of a shape or area.

**Perimeter** is a boundary line measure commonly used with shapes.

In **inequalities**, an algebraic expression stating that two values are not the same, the graph of the line (as if it were an equation) creates the boundary line for solutions of the inequality. The boundary line is dotted/dashed is the inequality includes only < or >; however, if *or equal to* is included, the line is drawn solid and points on the line are included in the solutions.

To unlock this lesson you must be a Study.com Member.

Create your account

Are you a student or a teacher?

Already a member? Log In

BackWhat teachers are saying about Study.com

Already registered? Log in here for access

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

You are viewing lesson
Lesson
1 in chapter 5 of the course:

Back To Course

Geometry for Kids6 chapters | 45 lessons

{{courseNav.course.topics.length}} chapters | {{courseNav.course.mDynamicIntFields.lessonCount}} lessons | {{course.flashcardSetCount}} flashcard set{{course.flashcardSetCoun > 1 ? 's' : ''}}

- Analytics 103: Intro to Relational Databases & SQL
- Praxis Special Education (5543): Practice & Study Guide
- School Leaders Licensure Assessment (SLLA): Study Guide & Practice
- Series 7 Exam: Study Guide & Practice
- Praxis Core Academic Skills for Educators - Combined Test (5752): Study Guide & Test Prep
- Using Views, Indexes & Triggers in SQL
- Introduction to SQL Syntax & Queries
- Joins & Subqueries Using SQL
- Relational Database Management Systems
- Introduction to General & Relational Databases
- What Is An Online Homeschool?
- Should I Homeschool My Children?
- Real Estate License Test Cost
- Top Blogs for New Homeschool Parents
- CEOE Test Retake Policy
- Study.com Customer Service FAQs: Login, Cost & Support Email
- Study.com Refund: How to Request a Refund from Study.com

- How to Find a Prepositional Phrase
- Gains from Trade: Definition & Example
- Matilda by Roald Dahl Setting
- Dorsal Body Cavity: Definition, Organs & Membranes
- Understanding Michigan Usury Law
- How to Construct a Circle With a Compass
- Decimal Place Value to the Trillions
- Fractions As Parts of a Whole: Quiz & Worksheet for Kids
- Quiz & Worksheet - Figurative Language in Anne Frank's Diary of a Young Girl
- Quiz & Worksheet - Migration Consequences
- Quiz & Worksheet - Soil Science Facts for Kids
- Flashcards - Real Estate Marketing Basics
- Flashcards - Promotional Marketing in Real Estate
- 3rd Grade Math Worksheets & Printables
- Free Lesson Plans

- Soft Skills for IT Professionals
- Common Core Math Grade 8 - The Number System: Standards
- Georgia Milestones - American Literature & Composition EOC: Test Prep & Practice
- Honors Precalculus Textbook
- MTTC Communication Arts (Secondary)(091): Practice & Study Guide
- WEST Business & Marketing Education: Social Responsibility in Business
- PLACE Business Education: Hiring and Staffing
- Quiz & Worksheet - Woodwind Instruments
- Quiz & Worksheet - Characteristics of Fluorine
- Quiz & Worksheet - Comparing Random Sampling & Quota Sampling
- Quiz & Worksheet - Function and Structure of a Nucleoid
- Quiz & Worksheet - Methods for Teaching ELL Students

- Sigmund Freud's Layers of the Self
- Romeo and Juliet Prologue Activities
- How to Pass an AP Class
- How to Pass an AP Class
- What is a Good PSAT Score for a Sophomore?
- Average LSAT Score
- Scholarships for Homeschoolers
- Kentucky Homeschool Laws
- Memoir Writing Prompts
- Jobs for Retired Teachers
- Thanksgiving Bulletin Board Ideas
- Free PSAT Practice Test

- Tech and Engineering - Videos
- Tech and Engineering - Quizzes
- Tech and Engineering - Questions & Answers

Browse by subject