Let P1=I=100010001,P2=100001010,P3=010100001P4=010001100,P5=001100010,P6=001010100 and X=∑k=16Pk213102321PkTWhere PkT denotes the transpose of the matrix Pk. Then which of the following options is/ are correct?
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a
X is a symmetric matrix
b
The sum of diagonal entries of X is 18
c
X – 30I is an invertible matrix
d
If X111=α111, then α=30
answer is A.
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Detailed Solution
Let A=213102321⇒X=∑k=16PkAPkT, Here PkPkT=PkTPk=I for all k=1,2,3,4,5,6 . PkT=Pk-1&AT=A and XT=∑k=16PkAPkTT=∑k=16PkAPkT=X Let B=111⇒XB=∑K=16PKAPKTB=∑K=16PKAB=∑K=16PKAB=222222222AB=303030=30111=30B∴α=30 and (X-30I) is singular, Tr∑k=16PkAPkT=18