Math Is Fun Forum

johnathon2

Real Member

Registered: 2007-09-28

Posts: 15

pre-algebra

what is k my math teacher is even stumped plese help she says it might be

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mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: pre-algebra

I'm guessing that's

.

If so, then that's the same as

.

So now you solve

or, alternatively,

.

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It wanted to be normal.

johnathon2

Real Member

Registered: 2007-09-28

Posts: 15

Re: pre-algebra

my math teacher says that that that should not be in my lessson i ttake it online and she says thatis too advanced  the site it is on is www.auroralearning.com you cant get on with out a password but hve you evey heard of it she also says that the problem it that the question it like a  algabra 2 question

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NullRoot

Member

Registered: 2007-11-19

Posts: 162

Re: pre-algebra

That is a tough one for pre-algebra if you haven't learned the laws of rational exponents. Here's another way to look at it:

If you know the rules of rational exponents, then:

(³√k)² = (³√k)*(³√k)
So:
k = -2*(³√k)*(³√k)

This part you can use some reasoning for. "k" should be equal to its cube root * its cube root * its cube root, right?
So if the problem above shows that cube root k * cube root k * -2 = k, then that must mean -2 is the cube root of k.
That then means (-2)³ = k, or -2*-2*-2 = -6 = k.

EDIT: As per below, (-2)³ is, in fact, -8, not -6.

Last edited by NullRoot (2007-12-07 11:43:50)

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Trillian: Five to one against and falling. Four to one against and falling… Three to one, two, one. Probability factor of one to one. We have normality. I repeat, we have normality. Anything you still can’t cope with is therefore your own problem.

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: pre-algebra

That then means (-2)³ = k, or -2*-2*-2 = -6 = k.

-6? typo i'm guessing.. should be -8.

NullRoot

Member

Registered: 2007-11-19

Posts: 162

Re: pre-algebra

Yep. Well spotted

I still get credit for solving for k without actually doing anything more than rearranging the equation, though, right?

Last edited by NullRoot (2007-12-07 11:42:45)

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Trillian: Five to one against and falling. Four to one against and falling… Three to one, two, one. Probability factor of one to one. We have normality. I repeat, we have normality. Anything you still can’t cope with is therefore your own problem.