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Solve x^3 = 8

Step by step, with the reason for every step · Solve x² = 49 and x³ = 27 · Foundations

Step by step

The question

Question: solve x³ = 8.

x3 = 8

x³ means x times x times x.

We want just x.

x³ = x × x × x

1 Cube root of both sides

The cube root asks: which number, times itself three times, makes this?

∛27 = ? → ? × ? × ? = 27

The cubes: 1 times 1 times 1 is 1.

2 times 2 times 2 is 8.

3 times 3 times 3 is 27.

1³ = 1, 2³ = 8, 3³ = 27

x is the cube root of 8.

x = 3√8

2 times 2 times 2 is 8.

So x = 2.

x = 2

Careful!

A cube has one answer, not two.

Minus 2, cubed, is minus 8.

Not like x² = 49.

Careful: not x = 2 or x = −2 ✗

2 Check

Let's check: 2 times 2 times 2 is 8.

2 × 2 × 2 = 8

The same as the right side.

So the answer is right!

Let's look back.

First: cube root of both sides.

Last: check.

Answer
Careful: not x = 2 or x = −2 ✗

Your turn

Try this one yourself, then check:

Solve x3 = 27
Show the answer
x = 3

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