This course begins with the cube of a number and the cubes from 1 to 20, then shows why the cube of a negative number is negative and how to add and take away cubes. You cube fractions by cubing the top and the bottom, and decimals by counting places. Next comes the cube root as the opposite of cubing: you find it by grouping prime factors in threes, test whether a number is a perfect cube, and learn a quick last-digit method. The course ends with cube roots of negative numbers, fractions and decimals, and the rules that connect them.
Primary Years
Cubes and Cube Roots
Cubes of whole numbers, negative numbers, fractions and decimals, and cube roots found by grouping prime factors in threes, by a last-digit short cut and by the rules of cube roots.
- 4 lessons
Overview
Lessons
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Cubes of numbers
What a³ means, the cubes from 1 to 20, patterns in their last digits, why the cube of a negative number is negative, and how to add and take away cubes.
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Cubes of fractions and decimals
Cube a fraction by cubing its top and bottom, cube a mixed number by first making it improper, and cube a decimal by giving the answer three times as many places.
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Cube roots
The cube root undoes cubing. Find cube roots by grouping prime factors in threes, test for perfect cubes, and find the cube root of a perfect cube from its last digit.
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Properties of cube roots
Cube roots of negative numbers, the rules for products and fractions, cube roots of decimals and mixed numbers, and why you cannot add under one root.
Practice papers
Ten question papers that follow the lessons in order. Each has 20 questions for 50 marks (1 hour 30 minutes), with a key sheet and worked solutions.
MCQ tests
Ten tests of 25 multiple-choice questions (30 minutes each). Answer them on the page and check your score, or download the PDF with its key and solutions.
Class notes
Cubes and Cube Roots
Typed from the teacher's handwritten class slides, 3 pages.
Download the notes (PDF, 108.6 KB)