kinda hard exponent problem

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September 16th 2011, 07:33 AM
jsvlad

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kinda hard exponent problem

q23 (answer 4)

Given 2x^2 = 3y^3

By how much will y increase if x is multiplied by 2?

1) 2^(1/3)
2) 4^(1/3)
3) 8

Attachment 22287

thanks in advance!
September 16th 2011, 08:38 AM
Siron

Re: kinda hard exponent problem

Reform the given equation to $y=...$
Afterwards replace $x$ by $2x$ .
Then you'll see $y$ is increased by a factor ... ?
September 16th 2011, 08:44 AM
jsvlad

Re: kinda hard exponent problem

y= (2/3x^2)^(1/3)
2^2=4
4*2/3 = 8/3
8/3^(1/3)
isn't an answer option... grrr
that 3 keeps bugging me out!
September 16th 2011, 08:50 AM
Siron

Re: kinda hard exponent problem

What I mean is the following:
$2x^2=3y^3$
$\Leftrightarrow y=\sqrt[3]{\frac{2x^2}{3}}$ (1)
Because the question asks how y increases if x is multiplied by two you have to replace x by 2x
$\Leftrightarrow y=\sqrt[3]{\frac{2(2x)^2}{3}}$
$\Leftrightarrow y=\sqrt[3]{\frac{2\cdot 4x^2}{3}}$
$\Leftrightarrow y=\sqrt[3]{4}\cdot \sqrt[3]{\frac{2x^2}{3}}$ (2)

So you recognize an equal part in (1) and (2), but (2) is multiplied by a factor ... ?
September 16th 2011, 11:39 AM
jsvlad

Re: kinda hard exponent problem

I thought I read The problem wrong. That's why I included the image. Again I don't know the answer. I got the same reasoning solution as you
September 16th 2011, 11:41 AM
e^(i*pi)

Re: kinda hard exponent problem

Quote:

Originally Posted by jsvlad

I thought I read The problem wrong. That's why I included the image. Again I don't know the answer. I got the same reasoning solution as you

If you understand how Siron got that answer then use your laws of exponents to say that $\sqrt[3]{4} = 4^{1/3}$

Edit: The question is asking to find the difference in "scale" if you will. In other words it wants you to find $\dfrac{f(2x)}{f(x)}$ where f(x) is the equation given.

From Siron's post the answer is eq2/eq1