Hi, this is my first post so I hope I get it right.

I'm a 3rd year engineering student from Sydney, Australia.

I'm just starting

*multi*variable calculus and am a little unsure. Here's my question and solution.

Could someone please confirm where/if I'm going wrong?

(Should read 'Let u = (4-x^2-y^2)^1/2). I forgot to put in the power of 1/2.

EDIT: Oh no! I just saw another mistake. I shouldn't have a 4 in the last line of either function as it's constant. Sorry guys...

What I'm basically 'trying' to do is apply the chain rule as with a single variable problem but when substituting (4-x^2-y^2) into u (last 2 lines) I'm letting the variable I'm not dealing with become a constant and thus = 0.

Ie for f'(x), y = 0 and for f'(y) x=0.

(This is why I have (4-0-y^2) in the last line of f'(y). I didn't put the zero into the f'(x) but maybe should have to make my thinking more clear.