Mathematics › Matrices › Adjoint and its Properties
Given, A=mnpq, A-dadjA=0
Here, d=|A|=mq-np
⇒A-dadjA=mnpq-dq-n-pm=0
⇒m-qdn1+dp1+dq-md=0
⇒m-qdq-md-np1+d2=0
⇒mq-m2d-q2d+mqd2-np1+2d+d2=0
⇒mq-m2d-q2d+mqd2-np-2npd-npd2=0
⇒mq-np+d2mq-np-dm2+q2+2np=0
⇒(mq-np)(1+d2)-d(m+q)2=0
⇒1+d2=d(m+q)2(mq-np)
⇒1+d2=(mq-np)(m+q)2(mq-np) ∵ d=mq-np
⇒1+d2=m+q2
Hence, option A is correct.
Asked in: JEE Main 2023 (30 Jan Shift 1)
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