I’m doing a geophysics module at the moment and not having done any trig-related maths for decades, I’m struggling with what are some fairly basic stuff.

I can derive results from equations, but the difficulty comes when rearranging equations to derive a different function.

As an example, the basic equation is: sin i/sin r = v1/v2

I’m familiar with the basics of trig, i.e. SOCAHTOA, but i’s mainly the rearranging thing.

You’ve also got t = 2h/(V1 cosiC) + (x – 2h tan iC)/V2
(time taken for head wave)

I understand the principles of Snells Law, and the whole thing with refraction and relfection. However, it’s the maths I’m having a bit of a blank with at the moment.

Does anyone have any Snell’s Law for dummies tips or guides?

Snell?

Snell?

Achtung! For you Tommy ze war is over.

So your issue isn’t with the concept but more with the rearranging of the equation to find a value etc?

So your issue isn’t with the concept but more with the rearranging of the equation to find a value etc?

Yep.

Well that’s not singular to Snell it’s just lack of familiarity with algebraic functions and how to manipulate them to get what you want. I’ve got friends doing geology and similar subjects at uni and they have very little background or struggle to remember how, for them it was more of a case of repetition more than any specific tricks.

If you start by just looking at more basic equations and re-arranging them you refamiliarise yourself with the technique and start to understand the main problem which is understanding how one element of the equation ties in/relates/has an affect on other elements.

At it’s core it’s understanding the relationships between different components of the equation.

Well that’s not singular to Snell it’s just lack of familiarity with algebraic functions and how to manipulate them to get what you want

Yes, absolutely. I just thought I’d give it a bit of context.

It’s not much help but I’ve been having to relearn all these trigonomic functions to help my daughter out with her A-level maths, been a long time 😀

One thing that might be of use is pretty obvious, but you might not have thought of it: Google. Type the full equation in and you often find there’s a helpful page explaining how it’s derived.

Thankfully I only finished A Levels 3 years ago so it’s still pretty familiar. Seeing how something is derived can often help your understanding if it’s parts and how to rearrange them.

How exactly do you want to rearrange the equations?

How exactly do you want to rearrange the equations?

To be able to calculate any of the functions e.g. rearrange snell’s law to find sin r, or maybe v1

sin i/sin r = v1/v2

sin i = sin r*v1/v2
sin i*v2 = sin r*v1
sin i*v2/v1 = sinr
OR
sin i*v2/sin r = v1

Someone sanity check that for me.

Looks correct.

Equations are just a set of scales. Do the same to both sides and you will keep balanced.

Also from trig work remember tan = sin/ cos.

Thanks folks, that makes sense.

I think I’m now ok with rearranging simple equations, but more complicated ones give still result in a dark cloud descending. I guess it’s a case of just becoming familiar again with the language.

If it’s any consolation I have been a geophysicist for <mumble> years and I still have to work this stuff out from the basics.

mikey – this is a great book and directly relevant for the course as a whole:

Mathematics: A Simple Tool for Geologists

http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0632053453.html

Ah geofiction 😛 Speaking as a geologist it’s borderline witchcraft as far as I’m concerned.