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NDA 2020
Exam
NDA
Year
2020
Subject
Mathematics
Chapter
Matrices

NDA 2020 · Mathematics · Matrices

If matrix A=[ array cc 1-i & i -i & 1-i array ] where i= -1 , then...

If matrix A=\left[1−ii−i1−i\begin{array}{cc}1-i & i \\ -i & 1-i\end{array}\right] where i=−1i=\sqrt{-1}, then which one of the following is correct?

Options

  1. AAA is hermitian
  2. BAA is skew-hermitian
  3. C(Aˉ)T+A(\bar{A})^T+A is hermitian
  4. D(Aˉ)T+A(\bar{A})^T+A is skew-hermitian

Correct answer

C. (Aˉ)T+A(\bar{A})^T+A is hermitian

Step-by-step solution

A square MM matrix is said to be Hermitian (or selfadjoint) if it is equal to its. Own Hermitian conjugate, i.e. (Mˉ)T=M(\bar{M})^T=M Given Matrix A=\left[1−ii−i1−i\begin{array}{cc}1-i & i \\ -i & 1-i\end{array}\right](\bar{A})^T=\left[1+ii−i1+i\begin{array}{cc} 1+i & i \\ -i & 1+i \end{array}\right]Now, A+(Aˉ)T=[1−ii−i1−i]+[1+ii−i1+i]=[22i−2i2]=2[1i−i1]\begin{aligned} & \text{Now, } A+(\bar{A})^T=\left[\begin{array}{cc}1-i & i \\ -i & 1-i\end{array}\right]+\left[\begin{array}{cc}1+i & i \\ -i & 1+i\end{array}\right] \\ & =\left[\begin{array}{cc}2 & 2 i \\ -2 i & 2\end{array}\right]=2\left[\begin{array}{cc}1 & i \\ -i & 1\end{array}\right]\end{aligned}ConjugatetransposeofConjugate transpose of\left(A+(\bar{A})^T\right)=2\left[1i−i1\begin{array}{cc}1 & i \\ -i & 1\end{array}\right] Hence, (A+(Aˉ)T)\left(A+(\bar{A})^T\right) is hermitian.
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