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Question: Answered & Verified by Expert
If $\left|\begin{array}{ccc}2 & 4 & 0 \\ 0 & 5 & 16 \\ 0 & 0 & 1+p\end{array}\right|=20$, then what is the value of $p$?
MathematicsDeterminantsJEE Main
Options:
  • A 0
  • B 1
  • C 2
  • D 5
Solution:
2661 Upvotes Verified Answer
The correct answer is: 1
$\left|\begin{array}{ccc}2 & 4 & 0 \\ 0 & 5 & 16 \\ 0 & 0 & 1+p\end{array}\right|=20$
On expanding along $\mathrm{C}_{1}$, $2\{5(1+p)-0\}=20$
$\Rightarrow 1+p=2$
$\Rightarrow p=1$

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