Partial Derivatives Z 805C24
1. **Problem statement:** Given the implicit equation $$x + y + z = \log z,$$ find the partial derivatives $$\frac{\partial z}{\partial x}$$ and $$\frac{\partial z}{\partial y}.$$
2. **Formula and rules:** For implicit differentiation, treat $$z$$ as a function of $$x$$ and $$y$$, i.e., $$z = z(x,y)$$. Differentiate both sides of the equation with respect to $$x$$ and $$y$$ separately, applying the chain rule where necessary.
3. **Differentiate with respect to $$x$$:**
$$\frac{\partial}{\partial x}(x + y + z) = \frac{\partial}{\partial x}(\log z)$$
Since $$y$$ is independent of $$x$$, $$\frac{\partial y}{\partial x} = 0$$. So,
$$1 + 0 + \frac{\partial z}{\partial x} = \frac{1}{z} \frac{\partial z}{\partial x}$$
4. **Rearrange to solve for $$\frac{\partial z}{\partial x}$$:**
$$1 + \frac{\partial z}{\partial x} = \frac{1}{z} \frac{\partial z}{\partial x}$$
Multiply both sides by $$z$$:
$$z + z \frac{\partial z}{\partial x} = \frac{\partial z}{\partial x}$$
Bring terms involving $$\frac{\partial z}{\partial x}$$ to one side:
$$z = \frac{\partial z}{\partial x} - z \frac{\partial z}{\partial x} = \frac{\partial z}{\partial x}(1 - z)$$
Therefore,
$$\frac{\partial z}{\partial x} = \frac{z}{1 - z}$$
5. **Differentiate with respect to $$y$$:**
$$\frac{\partial}{\partial y}(x + y + z) = \frac{\partial}{\partial y}(\log z)$$
Since $$x$$ is independent of $$y$$, $$\frac{\partial x}{\partial y} = 0$$. So,
$$0 + 1 + \frac{\partial z}{\partial y} = \frac{1}{z} \frac{\partial z}{\partial y}$$
6. **Rearrange to solve for $$\frac{\partial z}{\partial y}$$:**
$$1 + \frac{\partial z}{\partial y} = \frac{1}{z} \frac{\partial z}{\partial y}$$
Multiply both sides by $$z$$:
$$z + z \frac{\partial z}{\partial y} = \frac{\partial z}{\partial y}$$
Bring terms involving $$\frac{\partial z}{\partial y}$$ to one side:
$$z = \frac{\partial z}{\partial y} - z \frac{\partial z}{\partial y} = \frac{\partial z}{\partial y}(1 - z)$$
Therefore,
$$\frac{\partial z}{\partial y} = \frac{z}{1 - z}$$
**Final answers:**
$$\boxed{\frac{\partial z}{\partial x} = \frac{z}{1 - z}, \quad \frac{\partial z}{\partial y} = \frac{z}{1 - z}}$$