# Homework Help: Cube roots

1. Oct 27, 2007

### poohbear1986

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. Oct 27, 2007

### hotcommodity

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" ?

3. Oct 27, 2007

### poohbear1986

i was no given one, i think my teacher is a moron

4. Oct 27, 2007

### hotcommodity

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"?

5. Oct 27, 2007

### d_leet

It's the volume of a cube with side length s, I believe that s3 was meant to be s3.

6. Oct 27, 2007

### hotcommodity

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$$y = x^{4}$$ , then I can put x in terms of y by multiplying both x and y to the $$\frac{1}{4}$$ power:

$$y^{\frac{1}{4}} = x^{4*\frac{1}{4}}= x$$

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.

7. Oct 27, 2007

### poohbear1986

can you use numbers its easier to see what you mean

thanks

8. Oct 27, 2007

### hotcommodity

Sure, we can do that. If I say $$16 = x^{4}$$, then I want to multiply both sides of the equation by the one-fourth power:

$$16^{\frac{1}{4}} = x^{4*\frac{1}{4}}= x$$

Then just plug 16 to the 1/4 power into your calculator to find that x = 2.

9. Oct 27, 2007

### poohbear1986

still not understanding both sides of my equation are gooing to have cubed numbers

10. Oct 27, 2007

### hotcommodity

You have $$V = s^{3}$$. What power must you multiply both sides by to get s in terms of V? If you multiply$$s^{3}$$ by a certain power, you'll get s all by itself. Follow the reasoning in the example above.

11. Oct 27, 2007

### poohbear1986

so if i multiply both sides by 1/3 i should get what i'm looking for

12. Oct 27, 2007

### hotcommodity

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 $$81 = x^{4}$$ , I want to multiply each side by the 1/4 power to find x:

$$81^{\frac{1}{4}} = x^{4*\frac{1}{4}} = x$$

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.

13. Oct 27, 2007

### poohbear1986

thanks alot i finally understand what i'm looking at, i appreciate the help

14. Oct 27, 2007

### hotcommodity

No problem :) Keep up the good work.