Help Solve

It is a notation that is sometimes used, especially in more advanced work.  Not usually at secondary school level though.

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I assume f_y and f_z are partial derivatives with respect to y and z respectively.  If so, then

f = xy + ln(yz)

f_y = x +1/y

f_z = 1/z

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Thanks Alan,

I wasn't supposed to recognise this notation was I?

Thanks Alan