3 and 4 .Determinants and Matrices
easy

यदि  $A = \left[ {\begin{array}{*{20}{c}}i&0\\0&i\end{array}} \right]$ ओर $B = \left[ {\begin{array}{*{20}{c}}0&{ - i}\\{ - i}&0\end{array}} \right]$  तो $(A + B)(A - B)$

A

${A^2} - {B^2}$

B

${A^2} + {B^2}$

C

${A^2} - {B^2} + BA + AB$

D

इनमें से कोई नहीं

Solution

यहाँ $AB = \left[ {\begin{array}{*{20}{c}}i&0\\0&i\end{array}} \right]\,\left[ {\begin{array}{*{20}{c}}0&{ – i}\\{ – i}&0\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}0&1\\1&0\end{array}} \right]$       

तथा $BA = \left[ {\begin{array}{*{20}{c}}0&{ – i}\\{ – i}&0\end{array}} \right]\left[ {\begin{array}{*{20}{c}}i&0\\0&i\end{array}} \right]\, = \left[ {\begin{array}{*{20}{c}}0&1\\1&0\end{array}} \right]$

  चूकि $AB = BA,$  अत: $(A + B)(A – B) = {A^2} – {B^2}$. 

Standard 12
Mathematics

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