Euler-Lagrange equation application

[Ascendant78]

Homework Statement

Homework Equations

The Attempt at a Solution

I have tried manipulating the equation a few different ways, but the Euler-Lagrange and the one I'm supposed to show for a) is so different that I just can't seem to work. Can someone please point me in the right direction here?

 

[mfb]

I think you don't need the Euler-Lagrange equation for (a). That looks like the standard derivative, just calculate it.

 

[Ascendant78]

Well, just calculating the derivative, I'm not sure why it is coming out the way it is? I get that the "t" component would be zeros, cancelling out its parts. However, I'm not sure what derivative/partial derivative rules are being applied to get the equation to look like the one asked for in a)?

 

[vela]

Think chain rule. If you still can't figure it out, show us your attempt.