Q53 / 90 · JEE Main 2021 (26 Aug Shift 2) · Mathematics

Let A be a 3×3 real matrix. If det(2Adj(2Adj(Adj(2A))))=241, then the value of detA2 equals ______.

Correct answer: 4

Solution

∴|KA|=Kn|A|, If A is n×n matrix

|AdjA|=|A|n-1 If A is n×n matrix

|2Adj(2Adj(Adj(2A)))|=241

⇒23|Adj(2Adj(Adj(2 A)))|=241
⇒|Adj(2Adj(Adj(2 A)))|=238
⇒(|2Adj(Adj(2 A))|)2=238
⇒|2Adj(Adj(2 A))|=219
⇒23|Adj(Adj(2 A))|=219
⇒|Adj(Adj(2 A))|=216
⇒(|Adj(2 A)|)2=216
⇒|Adj(2 A)|=28
⇒|(2 A)|2=28
⇒|(2 A)|=24
⇒23| A|=24
⇒|A|=2

So, A2=A2=4

Hence, the correct answer is 4.

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