In [1, p. 35 exercise 2.15] we are asked to verify the formulas given for the gradient of a quadratic and linear form [1, p. 31 (2.61)]. The corresponding formulas are
 $\frac{\partial}{\partial \mathbf{x}}(\mathbf{x}^T\mathbf{A}^{\prime}\mathbf{x})=2\mathbf{A}^{\prime}\mathbf{x}$ (1)

and
 $\frac{\partial}{\partial \mathbf{x}}(\mathbf{b}^{\prime T}\mathbf{x})=\mathbf{b}^{\prime}$ (2)

where $\mathbf{A}^{\prime}$ is a symmetric $n \times n$ matrix with elements $a_{ij}$ and $\mathbf{b}^{\prime}$ is a real $n \times 1$ vector with elements $b_{i}$ and $\frac{\partial}{\partial \mathbf{x}}$ denotes the gradient of a real function in respect to $\mathbf{x}$. read the conclusion >