How to derive from this formula:
$\frac{\partial(\mathbf g.\mathbf h)}{\partial \mathbf x} = \left(\frac{\partial(\mathbf g.\mathbf h)}{\partial x_1},\frac{\partial(\mathbf g.\mathbf h)}{\partial x_2},\frac{\partial(\mathbf g.\mathbf h)}{\partial x_3}\right)^T=\ldots$
this formula:
$\ldots=\frac{\partial(\mathbf h^T)}{\partial \mathbf x}\mathbf g+\frac{\partial(\mathbf g^T)}{\partial \mathbf x}\mathbf h$