If P=⎡⎢⎣x 0 00 y 00 0 z⎤⎥⎦ and Q=⎡⎢⎣a 0 00 b 00 0 c⎤⎥⎦ then prove that
PQ=⎡⎢⎣xa 0 00 yb 00 0 zc⎤⎥⎦=QP
PQ=⎡⎢⎣x 0 00 y 00 0 z⎤⎥⎦ and Q=⎡⎢⎣a 0 00 b 00 0 c⎤⎥⎦=⎡⎢⎣xa 0 00 yb 00 0 zc⎤⎥⎦ ...(i)
and QP = ⎡⎢⎣a 0 00 b 00 0 c⎤⎥⎦⎡⎢⎣x 0 00 y 00 0 z⎤⎥⎦=⎡⎢⎣xa 0 00 yb 00 0 zc⎤⎥⎦ ..........(ii)
Thus, we see that, PQ = QP [using Eqs. (i) and (ii)]
Hence proved.