# Math Help - Question on derivative

1. ## Question on derivative

hi everyone,

Find $\frac{dz}{dx} and \frac{dz}{dy}$
xyz-cos(x+y+z)=0

i am having problems with the cos(x + y + z).

2. Originally Posted by anderson
hi everyone,

Find $\frac{dz}{dx} and \frac{dz}{dy}$
xyz-cos(x+y+z)=0

i am having problems with the cos(x + y + z).

What is your problems exactly in $cos(x+y+z)$ ?

3. hi General,

is this correct?

F(x,y,z) = xyz - cos(x + y + z)

$F_x$=yz+sin(x+y+z),

i dont know how to get sin(x+y+z), u = (x + y + z),i dont know how to continue from there to get sin(x+y+z)

thank you for all your help & support.

4. Originally Posted by anderson
hi General,

is this correct?

F(x,y,z) = xyz - cos(x + y + z)

$F_x$=yz+sin(x+y+z),

i dont know how to get sin(x+y+z), u = (x + y + z),i dont know how to continue from there to get sin(x+y+z)

thank you for all your help & support.

Sorry I will reply to this. Since General is offline.

Your $F_x$ is correct.

In general, If $h$ is differentiable, then:
$\frac{\partial}{\partial x}( \,\ cos( \, h(x,y,z) \, ) \,\ ) = -sin( \, h(x,y,z) \, ) \, \frac{\partial}{\partial x}( \, h(x,y,z) \, )$.

Did you get it ?