Unit 12 · Cubes and Cube Roots
Cubes and Cube Roots
Mathematics · Grade 7
What You Will Be Able To Do
🧊Cube any number and take the cube root of any perfect cube
⚡Read the last digit of a cube root straight off the number
🔢Find a cube root by grouping prime factors in threes
💧Explain why doubling a tank in every direction gives eight times the water
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A square number fills a flat square. A cube number fills a solid cube. Eight small blocks really do stack into a 2 by 2 by 2 cube.
Presenter notes: Open with blocks, exactly as the last lesson opened with counters. Hand each group a pile of sugar lumps or small wooden cubes and ask them to build the smallest solid cube they can that is bigger than a single block. They will build 2 by 2 by 2 and count 8. Ask for the next one up, and they will need 27. The jump from 8 to 27 is startling when you are holding the blocks, and that surprise is the whole subject of the lesson.