Question: How to differentiate to a variable in function of time

EDIT: My question has been  answered below

 

Hello,

Lets' say I have the equation L:

 

L= 

I want to take the partial derivative of L to diff(theta2(t), t). 

Maple doesn't allow me to do this: diff(L, diff(theta2(t),t));

How can I solve this problem?

 

I hope someone can help me. Thanks in advance!

Loïc

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