Which one of the following equations is a correct identity for arbitrary 3 × 3 real matrices P, Q and R?
A
P(Q + R) = PQ + RP
B
(P - Q)<sup>2</sup> = P<sup>2</sup> - 2PQ + Q<sup>2</sup>
C
det (P + Q) = det P + det Q
D
(P + Q)<sup>2</sup> = P<sup>2</sup> + PQ + QP + Q<sup>2</sup>
Correct Answer: (P + Q)<sup>2</sup> = P<sup>2</sup> + PQ + QP + Q<sup>2</sup>
