Let A = m n p q ,   d = A ≠ 0 and A - d Adj A = 0 . Then

Let A=mnpq, d=A0 and A-dAdjA=0. Then
  1. 1+d2=m+q2
  2. 1+d2=m+q2
  3. 1+d2=m2+q2
  4. 1+d2=m2+q2

Solution

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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