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Homework Help: Cube roots

  1. Oct 27, 2007 #1
    trying to figure this out, but am confused on the steps please help thank you

    The volume of a cube is given by V = s3, where s is the length of a side. Find the length of a side of a cube if the volume is 800 cm3. Round the answer to three decimal places.
  2. jcsd
  3. Oct 27, 2007 #2
    You already know the volume that you want (800cm^3). And you have an equation for the volume and the unknown(the unknown being s). Can you show me the equation you have for "s" in terms of "V" ?
  4. Oct 27, 2007 #3
    i was no given one, i think my teacher is a moron
  5. Oct 27, 2007 #4
    It looks like you were given one. You said in your opening post that the volume "V" is equal to 3 times "s," so you have V = 3s. Can you tell me what s equals in terms of "V"?
  6. Oct 27, 2007 #5
    It's the volume of a cube with side length s, I believe that s3 was meant to be s3.
  7. Oct 27, 2007 #6
    Ah, you're correct. My mistake.

    Well, for poohbears sake, I'll give an example of what your teacher is looking for.

    If I have[tex] y = x^{4} [/tex] , then I can put x in terms of y by multiplying both x and y to the [tex] \frac{1}{4} [/tex] power:

    [tex] y^{\frac{1}{4}} = x^{4*\frac{1}{4}}= x[/tex]

    Now I have x in terms of y. Just multiply both sides of your equation by a similar power to get s in terms of the volume. Sorry for any confusion.
  8. Oct 27, 2007 #7
    can you use numbers its easier to see what you mean

  9. Oct 27, 2007 #8
    Sure, we can do that. If I say [tex] 16 = x^{4} [/tex], then I want to multiply both sides of the equation by the one-fourth power:

    [tex]16^{\frac{1}{4}} = x^{4*\frac{1}{4}}= x[/tex]

    Then just plug 16 to the 1/4 power into your calculator to find that x = 2.
  10. Oct 27, 2007 #9
    still not understanding both sides of my equation are gooing to have cubed numbers
  11. Oct 27, 2007 #10
    You have [tex] V = s^{3} [/tex]. What power must you multiply both sides by to get s in terms of V? If you multiply[tex] s^{3} [/tex] by a certain power, you'll get s all by itself. Follow the reasoning in the example above.
  12. Oct 27, 2007 #11
    so if i multiply both sides by 1/3 i should get what i'm looking for
  13. Oct 27, 2007 #12
    Not by 1/3, but to the 1/3 power. Notice in the example above that we're multiplying both sides by a power. Here's one more to try:

    If I have [tex] 81 = x^{4}[/tex] , I want to multiply each side by the 1/4 power to find x:

    [tex] 81^{\frac{1}{4}} = x^{4*\frac{1}{4}} = x[/tex]

    When you plug in 81 to the one-fourth power, that is 81^(1/4), you should find that x = 3.Try the examples above on your calculator so you're comforable with the concept.
  14. Oct 27, 2007 #13
    thanks alot i finally understand what i'm looking at, i appreciate the help
  15. Oct 27, 2007 #14
    No problem :) Keep up the good work.
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