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in Linear Equations by (49.9k points)
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If A = \(\begin{pmatrix} cosθ&-sinθ \\ sinθ &cosθ \end{pmatrix}\) then A-1 = ?

A. A 

B. –A 

C. Adj A 

D. –adj A

1 Answer

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Best answer

A = \(\begin{pmatrix} cosθ&-sinθ \\ sinθ &cosθ \end{pmatrix}\)

│A│= cos2θ - (-sin2θ ) 

= cos2θ + (sin2θ ) = 1 ---------- (I) 

We know that A-1= 1/|A| adj A 

= adj A [From I]

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