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If A = \(\begin{pmatrix} cosα & sinα \\ -sinα & cosα \\ \end{pmatrix}\)be such that A + A ’ = I, then α =?

A. ∏ 

B. π/3

C. ∏

D.2π/3

1 Answer

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L.H.S: A + A' = \(\begin{pmatrix} cosα & sinα \\ -sinα & cosα \\ \end{pmatrix}\) + \(\begin{pmatrix} cosα & -sinα \\ sinα & cosα \\ \end{pmatrix}\)

This will be equal to \( ​​​​\begin{pmatrix} 1 & 0 \\ 0 & 1 \\ \end{pmatrix}\)

When 2cosa = 1 

cosa = 1/2

a = π/2

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