Question: Differentiate differential equation by function (Solving Lagrange 2 Equation)

Hi Maple friends,

I want to use Maple to solve a motion equation problem by using Lagrange 2 method. For that I for example have to calculate the derivative of the lagrange function by one of the generalized coordinates.

So let L for example be: L = diff(q1(t), t) + 2*diff(q2(t), t) + 3*q1(t)        // I`m sorry the insert Maple Math doesn`t work for me...

I now want to calculate diff(L,q1(t)) which leads to the error Message: "Error, invalid input: diff received q1(t), which is not valid for its 2nd argument".

The correct answer to this should be: diff(L, q1(t)) = 3

I`ve now tried a few different differentiate commands but none of them seems to work...

Would be great if someone could give me a hint or the right code.

Thanks in advance!