What is the derivative of Ax where A is a matrix and x is a vector?

I see two different formulae.


In this slides page 9, the derivative of $Ax$ is $A$.

But in some other documents such as http://faculty.arts.ubc.ca/vmarmer/econ627/vector%20diff.pdf. The derivative is $A^T$.

How to properly evaluate the derivative of Ax?

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