Derivative

[mark]

Hello everyone. I have a problem for the calculation of a time derivative of the kinetic energy. The calculator gives me a wrong result.
How can I do?
Thank you!

[Bisam]

The calculator can't know that

$mathjax$\theta'$mathjax$

is meant for the derivative of

$mathjax$\theta$mathjax$

.
Plus, you made the derivation relatively to

$mathjax$\theta$mathjax$

and not the time

$mathjax$t$mathjax$

...

If you want a correct answer with your calc using the chain rule, you must specify all variables for all functions.
E.g., here, you should type :

$mathjax$\dfrac{\partial}{\partial t}\left(12 m \cos(\theta(t))^2 \left(\dfrac{\partial}{\partial t}(\theta(t))\right)^2 r^2\right)$mathjax$

[mark]

thank you so much, I've been really help