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JEE Advanced 2012Paper 2
Exam
JEE Advanced
Year
2012
Paper
Paper 2
Subject
Mathematics
Chapter
Matrices

JEE Advanced 2012 · Paper 2 · Mathematics · Matrices

If P is a 3 × 3 matrix such that P^ T =2 P+I , where P^ T is the...

If PP is a 3×33 \times 3 matrix such that PT=2P+IP^{T}=2 P+I, where PTisthetransposeofP^{T} is the transpose ofPandandIistheis the3 \times 3identitymatrix,thenthereexistsacolumnmatrixidentity matrix, then there exists a column matrix\quad X=\left[xyz\begin{array}{l}x \\ y \\ z\end{array}\right] \neq\left[000\begin{array}{l}0 \\ 0 \\ 0\end{array}\right] such that

Options

  1. AP X=\left[000\begin{array}{l}0 \\ 0 \\ 0\end{array}\right]
  2. BPX=XP X=X
  3. CPX=2XP X=2 X
  4. DPX=−XP X=-X

Correct answer

D. PX=−XP X=-X

Step-by-step solution

PT=2P+IP^{T}=2 P+I ⇒P=2PT+I⇒P=2(2P+I)+I⇒P=4P+3I⇒P+I=0⇒PX+X=0⇒PX=−X\begin{array}{l} \Rightarrow P=2 P^{T}+I \Rightarrow P=2(2 P+I)+I \\ \Rightarrow P=4 P+3 I \Rightarrow P+I=0 \\ \Rightarrow P X+X=0 \Rightarrow P X=-X \end{array}
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