# Homework Help: Semi-major axis equation question

1. Jul 4, 2013

### eXmag

1. The problem statement, all variables and given/known data

Hi there, this isn't a homework question but I need some help with this equation since I'm not the best at mathematics. I would like to rearrange this equation so I can solve for "a"

2. Relevant equations

3. The attempt at a solution

?

2. Jul 4, 2013

### Dick

Well, start by squaring both sides. That will get rid of the square root. How bad at mathematics are you?

3. Jul 4, 2013

4. Jul 4, 2013

### Dick

Good to know. What happens if you try squaring both sides? Do your worst.

5. Jul 4, 2013

### eXmag

so you're saying

6. Jul 4, 2013

### Dick

That's pretty bad. You forgot to square the $2 \pi$. And if you square a square root then you eliminate the square root. $(\sqrt{x})^2=x$. Try and fix it up a little.

7. Jul 4, 2013

### eXmag

Ok then, another attempt.

8. Jul 4, 2013

### Dick

Closer. Just write $(2 \pi)^2$ instead of $2 \pi^2$. They mean different things don't they? I hope you know that much? The next step is to move everything except for $a^3$ to the left side of the equation. Know ANY algebra?

9. Jul 4, 2013

### eXmag

Well considering I haven't taken a math course since high school which was about 8 years ago so I'm a little rusty as you can tell. But it's starting to come back to me somewhat. So should this be the final solution then?

edit it should be (2pi)squared like u said

10. Jul 4, 2013

### Dick

Yes, that's right. Glad you got it if you write (2pi)^2. I didn't think you were going to make it for a while. Keep reviewing the algebra. It's not that hard and you need to know it.

11. Jul 4, 2013

### eXmag

OK, thanks for you're help!

12. Jul 4, 2013

### Dick

You're welcome. Um, it's 'your help' not 'you're help' if you want to do grammar too. :)