# Cosine Law Query?

1. Nov 29, 2013

### paolostinz

My online physics course is using cosine law to find the net forces on objects. My question is to do with the equation, at first it shows it as : c^2=a^2+b^2-2ab cosC.

From there, it changes to: c=[a^2+b^2-2ab cosC]^1/2.

How and why does this work? Why isn't a square root involved in the operation?

2. Nov 29, 2013

### R136a1

The notation $x^{1/2}$ is just another notation for $\sqrt{x}$. Was that your question?

3. Nov 29, 2013

### paolostinz

Yes, thank you! I see now, it seemed like I was getting the wrong answer when I was doing the original equation, so I thought something else was at play here.

Is there any reason why one would prefer writing the equation this way? I just don't get why my textbook would switch the equation when trying ton present new information.

4. Nov 29, 2013

### tiny-tim

hi paolostinz!
you mean, writing c instead of c2 ?

or writing (…)1/2 instead of √(…) ?

we usually want c itself, so the fact that it comes from an equation with c2 is a nuisance

(…)n is the general way of writing powers: there's no really good reason for having a special symbol when n = 1/2, and the bar of √, which should really go over the top of the bracket, is a nuisance when the bracket is long

5. Nov 29, 2013

### paolostinz

See, that makes sense, it's the little things like this that confuse me most. I wish I had better access to teachers to clear up these type of hiccups. I'm so grateful for this place, thank you everyone!