Find the total differential:

$\displaystyle u=arcsen \sqrt\frac{xz}{y}$

$\displaystyle du=?$

My teacher give to us this formule: $\displaystyle \Delta f (x,y) \approx \frac{\delta f}{\delta x} |p\Delta x + \frac{\delta f}{\delta y}|p\Delta y + \frac{\delta f}{\delta z}|p\Delta z$

but in this exercice he just dont give the point "P" and the valous of $\displaystyle \Delta n$

i use this formule: $\displaystyle \Delta f (x,y) \approx \frac{\delta f}{\delta x} + \frac{\delta f}{\delta y} + \frac{\delta f}{\delta z}$

and the result was:

part 1: http://i.imgur.com/W46hP.jpg

part 2: http://i.imgur.com/uYTek.jpg

is this correct??