Q.

let P=[31220α350] , where αR . Suppose Q=[qij]  is a matrix such that PQ=KI  where KR , K0 and I is the identity matrix of order 3. If  q23=K8  and det(Q)=K22  then which of the following option (s) is/are correct?

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a

det (Q adj(P)) = 213

b

4αK+8=0

c

α=0,K=8

d

det (P adj(Q)) = 29

answer is B, C.

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Detailed Solution

PQ = KI  PQK=IP1=QK
Also |P|=12α+20 
Comparing the third elements of 2nd row on both sides, we get
(3α+412α+20)=1k×K824α+32=12α+20α=1 
Since  |P|=8
Also PQ = KI  |P||Q|=K3 8×k22=k3k=4|Q|=k22=8
(B)  4αK+8=4×(1)4+8=0b±b24ac2a
(C) Now det (P adjQ) =  |P||adjQ|
=|P||Q|2=8×82=29 
(D) |QadjP|=|Q||P|2=29 

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let P=[3−1−220α3−50] , where α∈R . Suppose Q=[qij]  is a matrix such that PQ=KI  where K∈R , K≠0 and I is the identity matrix of order 3. If  q23=−K8  and det(Q)=K22  then which of the following option (s) is/are correct?