Since A=[02−20]
So A2=[02−20][02−20]=[−400−4]=−4I
and A3=−4A
Similarly A4=(−4I)(−4I)=(−4)2I,
A5=(−4)2A,A6=(−4)3I
Now M=k=1∑10A2k=A2+A4+….+A20
=[−4+(−4)2+(−4)3+….+(−4)20]I
=−k1I
So M is symmetric matrix
N=k=1∑10A2k−1=A+A3+……+A19
=A[1+(−4)+(−4)2+……+(−4)9]
=k2A
So N is skew symmetric
⇒N2 is symmetric matrix
Hence, MN2 is non-identity symmetric matrix