It should be rate of change of fx(x,y) w.r.t x (because second derivative is the rate of change of first derivative). This needs to be fixed at several places.
Are you referring to the first row?
f'_x(x,y) w.r.t. x
And you suggest to remove the apostrophe ( ’ ) of f?
I can’t see anything wrong in the equations because they are all second derivatives.
yes that’s my suggestion.
Currently I read it as: “rate of change of second derivative with respect to x” is d2f/dx2 (which is also second derivative). Not making sense, you see my point?
I understand the confusion.
f'_x(x,y) w.r.t. x
The notation above is read as “the rate of change of the first derivative with respect to x”