ShmoopTube

00:03

We’re about to throw an unshmoopy question your way… might want to duck…

00:07

Which of the following is the solution set to the equation… the absolute value of 3x – 6 = 21?

00:15

And here are the potential answers…

00:20

So… what is this question asking?

00:22

Can we calculate absolute volume problems with a variable?

00:26

For starters, let’s just ignore the absolute value piece…

00:28

…and solve for 3x minus 6 equals 21.

00:32

And add 6 to both sides...

00:34

We get 3x equals 27… so x is 9.

00:38

That’s if everything’s positive and rosy.

00:40

And since we KNOW that one of the solutions has to be 9, we can cross off A and D as potential answers.

00:47

The only question left is whether the negative 5 in choice C works as well.

00:52

So let’s… give it a spin.

00:54

And in this case we DO need to take the absolute value thing into account.

00:58

We have 3 times negative 5, which is negative 15 – then subtract 6 and we have negative 21.

01:07

But after we take the absolute value… we get positive 21.

01:11

And yeah… 21 equals 21… so negative 5 and 9 both work…

01:17

…and the answer is C.

01:18

As in, “Clear skies ahead.”

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