Pythagorean Theorem and Volume

Students learn about irrational numbers, approximating square roots of non-perfect square numbers, and investigate the well-known Pythagorean Theorem to solve for missing measures in right triangles.


Unit 7

8th Grade

Unit Summary

In Unit 7, 8th grade students extend their understanding of the Number System to include irrational numbers. This new understanding supports students as they study square and cube root equations and relationships between side lengths in right triangles, both concepts that fall within the major work of the grade. Students start the unit by investigating solutions to equations like $$x^2=2$$ and realize that the solution is not an exact point on the number line. They approximate square roots of non-perfect square numbers and represent rational numbers written in decimal form as fractions. The focus of the unit shifts to right triangles, and students investigate the well-known Pythagorean Theorem. They apply their understanding of square roots to solve for missing measures in right triangles and other applications. They look closely at geometric figures to identify and create right triangles, opening up the opportunity to apply the Pythagorean Theorem to find new information (MP.7). The focus shifts once more as students learn about cube roots and apply this new concept to various volume applications involving cylinders, spheres, and cones. Throughout the unit, students must attend to precision in their work, their solutions, and their communication, being careful about specifying appropriate units of measure, using the equals sign appropriately, and representing numbers accurately (MP.6). 

Prior to this unit, students learned many skills and concepts that prepared them for this unit. Since elementary grades, students have been learning about and refining their understanding of area and volume. They have learned how to use composition and decomposition as tools to determine measurements, they’ve learned formulas and how to use them in problem-solving situations, and they’ve encountered various real-world situations. Standard 8.G.9 is a culminating standard in the Geometry progression in middle school, which will lay the foundation for much of the work they will do in high school geometry

In high school, students will more formally derive the distance formula and other principles, they will expand their work with right triangles to include trigonometric ratios, and they will solve more complex problems involving volume of cylinders, pyramids, cones, and spheres.

Pacing: 20 instructional days (16 lessons (17 days), 2 flex days, 1 assessment day)

Fishtank Plus for Math

Unlock features to optimize your prep time, plan engaging lessons, and monitor student progress.


The following assessments accompany Unit 7.


Have students complete the Pre-Unit Assessment and Pre-Unit Student Self-Assessment before starting the unit. Use the Pre-Unit Assessment Analysis Guide to identify gaps in foundational understanding and map out a plan for learning acceleration throughout the unit.


Have students complete the Mid-Unit Assessment after lesson 11.


Use the resources below to assess student understanding of the unit content and action plan for future units.

Expanded Assessment Package

Use student data to drive instruction with an expanded suite of assessments. Unlock Pre-Unit and Mid-Unit Assessments, and detailed Assessment Analysis Guides to help assess foundational skills, progress with unit content, and help inform your planning.

Unit Prep

Intellectual Prep

Unit Launch

Before you teach this unit, unpack the standards, big ideas, and connections to prior and future content through our guided intellectual preparation process. Each Unit Launch includes a series of short videos, targeted readings, and opportunities for action planning to ensure you're prepared to support every student.

Internalization of Standards via the Post-Unit Assessment

  • Take the Post-Unit Assessment. Annotate for: 
    • Standards that each question aligns to
    • Strategies and representations used in daily lessons
    • Relationship to Essential Understandings of unit 
    • Lesson(s) that Assessment points to

Internalization of Trajectory of Unit

  • Read and annotate the Unit Summary.
  • Notice the progression of concepts through the unit using the Lesson Map.
  • Do all Target Tasks. Annotate the Target Tasks for: 
    • Essential Understandings
    • Connection to Post-Unit Assessment questions
  • Identify key opportunities to engage students in academic discourse. Read through our Teacher Tool on Academic Discourse and refer back to it throughout the unit.

Unit-Specific Intellectual Prep

Essential Understandings

  • The square root of $$p$$, or $$\sqrt{p}$$, represents a solution to the equation $$x{^2}=p$$. It is the measure of the side length of a square with an area of $$p$$ units$${^2}$$. The cube root of $$p$$, or $$\sqrt[3]{p}$$, represents a solution to the equation $$x{^3}=p$$. It is the measure of the side length of a cube with a volume of $$p$$ units$${^3}$$.
  • Every rational number can be expressed as a fraction $${a\over{b}}$$, where $$a$$ and $$b$$ are integers and $$b\neq0$$. As a decimal, every rational number either terminates or repeats. An irrational number has a decimal expansion that neither terminates nor repeats. For example, $${\sqrt2}$$ is an irrational number.
  • The Pythagorean Theorem describes the relationship between the side lengths of a right triangle. If a triangle is a right tringle, then $$ a{^2}+b{^2}=c{^2}$$, where $$a$$ and $$b$$ are the legs of the triangle and $$c$$ is the hypotenuse. The converse of the Pythagorean Theorem is also true. If the relationship $$ a{^2}+b{^2}=c{^2}$$ holds true for a triangle, then the triangle is a right triangle.
  • Many real-world problems can be modeled and solved using cylinders, cones, spheres, and other three-dimensional shapes.


converse statement


cube root



irrational number


perfect square

pythagorean triplet

pythagorean theorem

rational number


square root

To see all the vocabulary for Unit 7, view our 8th Grade Vocabulary Glossary.


  • Calculators (1 per student)
  • Graph Paper (1 sheet per student)
  • Poster paper (1 sheet per small group)
  • Scientific calculator (1 per student)

To see all the materials needed for this course, view our 8th Grade Course Material Overview.

Lesson Map

Topic A: Irrational Numbers and Square Roots

Topic B: Understanding and Applying the Pythagorean Theorem

Topic C: Volume and Cube Roots

Common Core Standards


Major Cluster

Supporting Cluster

Additional Cluster

Core Standards

Expressions and Equations

  • 8.EE.A.2 — Use square root and cube root symbols to represent solutions to equations of the form x² = p and x³ = p, where p is a positive rational number. Evaluate square roots of small perfect squares and cube roots of small perfect cubes. Know that √2 is irrational.


  • 8.G.B.6 — Explain a proof of the Pythagorean Theorem and its converse.
  • 8.G.B.7 — Apply the Pythagorean Theorem to determine unknown side lengths in right triangles in real-world and mathematical problems in two and three dimensions.
  • 8.G.B.8 — Apply the Pythagorean Theorem to find the distance between two points in a coordinate system.
  • 8.G.C.9 — Know the formulas for the volumes of cones, cylinders, and spheres and use them to solve real-world and mathematical problems.

The Number System

  • 8.NS.A.1 — Know that numbers that are not rational are called irrational. Understand informally that every number has a decimal expansion; for rational numbers show that the decimal expansion repeats eventually, and convert a decimal expansion which repeats eventually into a rational number.
  • 8.NS.A.2 — Use rational approximations of irrational numbers to compare the size of irrational numbers, locate them approximately on a number line diagram, and estimate the value of expressions (e.g., π²). For example, by truncating the decimal expansion of √2, show that √2 is between 1 and 2, then between 1.4 and 1.5, and explain how to continue on to get better approximations.

Foundational Standards

Expressions and Equations

  • 6.EE.B.5


  • 6.G.A.1
  • 6.G.A.3
  • 7.G.B.4
  • 7.G.B.6

The Number System

  • 6.NS.C.6
  • 7.NS.A.2.D
  • 7.NS.A.3

Future Standards

Expressing Geometric Properties with Equations

  • G.GPE.B.7

Geometric Measurement and Dimension

  • G.GMD.A.1
  • G.GMD.A.2
  • G.GMD.A.3

Similarity, Right Triangles, and Trigonometry

  • G.SRT.C.6
  • G.SRT.C.7
  • G.SRT.C.8

Standards for Mathematical Practice

  • CCSS.MATH.PRACTICE.MP1 — Make sense of problems and persevere in solving them.

  • CCSS.MATH.PRACTICE.MP2 — Reason abstractly and quantitatively.

  • CCSS.MATH.PRACTICE.MP3 — Construct viable arguments and critique the reasoning of others.

  • CCSS.MATH.PRACTICE.MP4 — Model with mathematics.

  • CCSS.MATH.PRACTICE.MP5 — Use appropriate tools strategically.

  • CCSS.MATH.PRACTICE.MP6 — Attend to precision.

  • CCSS.MATH.PRACTICE.MP7 — Look for and make use of structure.

  • CCSS.MATH.PRACTICE.MP8 — Look for and express regularity in repeated reasoning.

icon/arrow/right/large copy

Unit 6

Systems of Linear Equations


Unit 8

Bivariate Data

Request a Demo

See all of the features of Fishtank in action and begin the conversation about adoption.

Learn more about Fishtank Learning School Adoption.

Contact Information

School Information

What courses are you interested in?



Are you interested in onboarding professional learning for your teachers and instructional leaders?



Any other information you would like to provide about your school?

We Handle Materials So You Can Focus on Students

We Handle Materials So You Can Focus on Students

We've got you covered with rigorous, relevant, and adaptable math lesson plans for free