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 >