Differentiating an Equation: 2x Double Dot?

[likearollings]

Can anybody tell me how this is true.

THE FIRST X DOT IS SUPPOSED TO BE SQUARED!
http://img442.imageshack.us/img442/1264/80680201.jpg
THE FIRST X DOT IS SUPPOSED TO BE SQUARED!(I was given an equation and this is the LHS. I had to differentiate it with respect to x (i think) and this is the result, what is where the ... is?) I had to differentiate an equation and show it equaled another. I have got the RHS right, just can't work out how the LHS goes to 2x double dot

Any help is appreiciated

I suspect the chain rule is involved

 

[homology]

Hmmm, good question, I can get it if I play with differentials..

 

[likearollings]

Hmmm, good question, I can get it if I play with differentials..

is it even right? please have a play