Cogito
Grade 8 Math · Chapter 8 · Lesson 2
Cube Roots
The side length of a cube.
10 problems · about 18 minutes · 8.EE.A.2
What this lesson teaches
The child evaluates cube roots and distinguishes them from square roots.
- A cube root asks which number multiplied by itself three times gives the value.
- It is the edge length of a cube with that volume.
- Cube roots of negative numbers exist; square roots of negatives do not.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Square Roots and Irrational Numbers: What is √100?
Answer 10
Why 10.
Review — Calculating in Scientific Notation: (4 × 10⁵) × (2 × 10³). What is the exponent?
Answer 8
Why 8.
Review — Zero and Negative Exponents: What is 10⁻²? Give it as a decimal.
Answer 0.01
Why 0.01.
Warm Up
Straightforward practice. Get the method working first.
3 problemsCube root of 216?
Answer 6
Why 6.
Cube root of 8?
Answer 2
Why 2 × 2 × 2.
Cube root of 1000?
Answer 10
Why 10 × 10 × 10.
Build It Up
The same ideas with more to keep track of.
2 problemsSquare root of 49?
Answer 7
Why Two equal factors.
Cube root of −64?
Answer -4
Why (−4)³.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Cube: A cube has volume 125. What is its edge length?
Answer 5
Why 5.
The Negative: What is the cube root of −27?
Answer -3
Why −3.