Derivative of a vector-argument function

Hello!

Could you please help me as I am a newbie in the Mathcad world.
For a university homework, I was trying to solve some simple linear programming tasks (which I did).

However, something goes wrong when I am trying to find the partial derivative of a function which I define as R(y):= cT * y.

And 'c' is a 2D vector.

y is supposed to be from R^2, but I guess, MathCAD doesn't just get it and treats y as a scalar. Am I right? Is there a way to tell MathCAD that y is indeed a 2D vector?

My objective: I want to find d/dy_1 and d/dy_2 of R separately, or at least get a 2D vector containing these derivatives at a particular point.

What should I do? Is there a way to do it without redefining the function?

Please see the attached file for the details.

Thank you so much in advance!

Yours,
P.