Q.

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

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a

α=0, k=8

b

4α− k+8=0

c

det(Padj(Q))=29

d

det(Qadj(P))=213

answer is B.

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Detailed Solution

PQ=KI⇒PQ≠0⇒Q=KP−1P=12α+20∴K22=K3112α+20Q=KP−1=K12α+205α10-α3α6-3α-4-10122Q23=−k8=−k(3α+4)12α+20⇒α=-1,k=4|P(AdjQ)|=|P‖Q|2     since Q=kP-1=k3P-1=k3P=K6P=29Q(AdjP)=QP2=K3P=29
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