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Solve x^3 = 1/64

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

Step by step

The question

Question: solve x³ = 1/64.

x3 = 164

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.

4 times 4 times 4 is 64.

1³ = 1, 2³ = 8, 3³ = 27, 4³ = 64

x is the cube root of 1/64.

x = 3√164

We take the cube root of the top and of the bottom.

1 cubed is 1.

4 cubed is 64.

x = 3√13√64

So x = 1/4.

x = 14

Careful!

A cube has one answer, not two.

Minus 1/4, cubed, is minus 1/64.

Not like x² = 49.

Careful: not x = 14 or x = −14 ✗

2 Check

Let's check: 1/4 times 1/4 times 1/4 is 1/64.

14 × 14 × 14 = 164

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 = 14 or x = −14 ✗

Your turn

Try this one yourself, then check:

x3 = 127
Show the answer
x = 13

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