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Solve 27^x = 9

Step by step, with the reason for every step · Exponential equations and logarithms · Algebra 2

Step by step

The question

Question: solve 27 to the power x = 9.

x is up in the power.

27x = 9

1 Write both as powers of 3

27 is 3³, and 9 is 3².

We write both as powers of 3.

3 × 3 × 3 = 27
3 × 3 = 9

So 27 becomes 3³, and 9 becomes 3².

(33)x = 32

A power of a power: multiply the powers.

(am)n = am × n

The powers multiply: 3 times x is 3x.

33x = 32

2 The powers are equal

Both sides are 3 to a power.

Same base, and they are equal.

So the powers must be equal too.

same base → same power

Now we have 3x = 2.

3x = 2

3 Remove the 3

3x means 3 times x.

We want just x.

To remove times 3, we divide by 3.

We do it on both sides.

Why both sides?

The = sign means both sides are the same amount.

If we change only one side, they are not the same any more.

3x3 = 23

3 divided by 3 is 1.

So just x is left.

So x = 2/3!

x = 23

4 Check

Let's check: put 2/3 in place of x.

Check: 2723 = (33)23 = 32 = 9

We get 9, the same as the right side.

So x = 2/3 is right!

Let's look back.

First: write both as powers of 3.

Then: the powers are equal.

Then: remove the 3.

Last: check.

Answer
x = 23

Your turn

Try this one yourself, then check:

Solve 27x = 729
Show the answer
x = 2

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