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Can someone please tell me why when using the partial differentiation (accessed via the "Units" key) the Cos(A) is not represented in the answer?

d/dc ((b^2)+(c^2)-2*b*c*cos(A))^(1/2)

A-Z are predefined, numerical value variables in the home screen.

If you use capital A, even in the CAS screen, it will substitute the value for A in. Try it again with a lowercase a and it might work.

If that isn't it, can you post your screen or more steps?