If $\mathbf { r } = x \mathbf { i } + y \mathbf { j } + z \mathbf { k }$ and $f ( x , y , z ) = \ln | \mathbf { r } |$ , compute $\nabla f$ and determine where $f = 0$ and where $\nabla f = 0$ . What is the domain of f ?

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The Answer of If $\mathbf { r } = x \mathbf { i } + y \mathbf { j } + z \mathbf { k }$ and $f ( x , y , z ) = \ln | \mathbf { r } |$ , compute $\nabla f$ and determine where $f = 0$ and where $\nabla f = 0$ . What is the domain of f ?

If r=xi+yj+zk\mathbf { r } = x \mathbf { i } + y \mathbf { j } + z \mathbf { k }r=xi+yj+zk

If $\mathbf { r } = x \mathbf { i } + y \mathbf { j } + z \mathbf { k }$