Instead of (7.51):
$$\mathcal{D}(\boldsymbol{\lambda}) = -\frac{1}{2}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})^T\mathbf{A}\mathbf{Q}^{-1}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})-\mathbf{\lambda}^T\mathbf{b}$$
It should be:
$$\mathcal{D}(\boldsymbol{\lambda}) = -\frac{1}{2}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})^T\mathbf{Q}^{-1}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})-\mathbf{\lambda}^T\mathbf{b}$$
Describe the mistake The formulas for the dual optimization problem to a quadratic program contain an incorrect extra $\mathbf{A}$.
Location 6th printing; Chapter 7; Page 216; Equations 7.51 & 7.52
Proposed solution
Instead of (7.51): $$\mathcal{D}(\boldsymbol{\lambda}) = -\frac{1}{2}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})^T\mathbf{A}\mathbf{Q}^{-1}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})-\mathbf{\lambda}^T\mathbf{b}$$
It should be: $$\mathcal{D}(\boldsymbol{\lambda}) = -\frac{1}{2}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})^T\mathbf{Q}^{-1}(\mathbf{c}+\mathbf{A}^T\mathbf{\lambda})-\mathbf{\lambda}^T\mathbf{b}$$
Likewise for 7.52.