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Solve 2 × 3^x = 18

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

Step by step

The question

Question: solve 2 times 3 to the power x = 18.

x is up in the power.

2 × 3x = 18

Careful!

The power is only on the 3.

Powers come before times.

So we can't join 2 and 3 first.

Careful: not 2 × 3x = 6x ✗

1 Get the power alone

First the power must be alone: nothing added to it, nothing times it.

first: the power alone

The power is times 2.

To remove times 2, we divide by 2.

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.

2 × 3x2 = 182

2 divided by 2 is 1.

So just the power is left.

18 divided by 2 is 9.

Now we have 3ˣ = 9.

3x = 9

2 Write 9 as a power of 3

9 is 3 times itself, 2 times.

3 × 3 = 9

So 9 is 3².

Now both sides are 3 to a power.

3x = 32

3 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

So x = 2!

x = 2

4 Check

Let's check in the question: put 2 in place of x.

Check: 2 × 32 = 2 × 9 = 18

We get 18, the same as the right side.

So x = 2 is right!

Let's look back.

First: get the power alone.

Then: write 9 as a power of 3.

Then: the powers are equal.

Last: check.

Answer
x = 2

Your turn

Try this one yourself, then check:

Solve 3 × 3x = 27
Show the answer
x = 2

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