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Solve 4x^3 = 500

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

Step by step

The question

Question: solve 4x³ = 500.

4x3 = 500

x³ means x times x times x.

We want just x.

x³ = x × x × x

1 Remove the 4

4x³ means 4 times x³.

We want just x³.

To remove times 4, we divide by 4.

We do it on both sides, so they stay equal.

4x34 = 5004

4 divided by 4 is 1.

So just x³ is left.

500 divided by 4 is 125.

Now we have x³ = 125.

x3 = 125

2 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.

5 times 5 times 5 is 125.

1³ = 1, 2³ = 8, 3³ = 27, 4³ = 64, 5³ = 125

x is the cube root of 125.

x = 3√125

5 times 5 times 5 is 125.

So x = 5.

x = 5

Careful!

A cube has one answer, not two.

Minus 5, cubed, is minus 125.

Not like x² = 49.

Careful: not x = 5 or x = −5 ✗

3 Check

Let's check: 5 times 5 times 5 is 125.

5 × 5 × 5 = 125

4 times 125 is 500.

The same as the right side.

So the answer is right!

4 × 125 = 500

Let's look back.

First: remove the 4.

Then: cube root of both sides.

Last: check.

Answer
Careful: not x = 5 or x = −5 ✗

Your turn

Try this one yourself, then check:

Solve 5x3 = 320
Show the answer
x = 4

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