- #1

sa1988

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## Homework Statement

NOTE - When I post the thread my embedded images aren't showing up on my web browser, but they do show up when I bring it up to edit, so I don't know if other users can see the pictures or not... If not, they're here:

Problem outline: http://tinypic.com/r/34jeihj/9

Solution: http://tinypic.com/r/algpqh/9

## Homework Equations

## The Attempt at a Solution

[/B]

Given that x and x

^{2}in the Lagrangian don't need expanding, I simply took the Sin and Cos parts up to their x

^{2}terms and replaced them accordingly in the Lagrangian. However the given solution (below) seems to have done things rather differently. In particular I notice the 4a

^{2}x

^{2}term and the Sin term have both become zero.

Can anyone explain why this is? Some obvious algebra error on my part, or a fundamental aspect of Taylor expansions that I haven't properly grasped? Many thanks.