Let $A, B \in \mathbb{R}^{N \times M}$ each be a D4571: Real matrix.
Let $\alpha, \beta \in \mathbb{R}$ each be a D993: Real number.
Let $\alpha, \beta \in \mathbb{R}$ each be a D993: Real number.
Then
\begin{equation}
\mathsf{tr}(\alpha A + \beta B) = \alpha \mathsf{tr}(A) + \beta \mathsf{tr}(B)
\end{equation}