Anyone do degree level Economics?

[Barks]

Does anyone know how to get from (10.12) to (10.13) in the following. It doesn't make sense, it doesn't follow any form of differentiation I've ever seen before. Can anyone explain this? I'd be extremely grateful!

http://www.glowfoto.com/static_image/07-093321L/6921/jpg/11/2010/img6/glowfoto

Ta

 

[iamTakeo]

I'm in honours economics, if you were doing a maths course you'd probably need to know, but not if your just doing economics, I'd just take the equation as it is.

 

[Barks]

I'm in honours economics, if you were doing a maths course you'd probably need to know, but not if your just doing economics, I'd just take the equation as it is.

So do you mean I should just learn that result and use it to apply to actual numerical examples and questons?