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If `{:A=[(cos theta,sintheta),(-sintheta,costheta)]:}," then "A^2=I`is true for

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If `{:A=[(cos theta,sintheta),(-sintheta,costheta)]:}," then "A^2=I`is true for
A. `theta=0`
B. `theta=pi/4`
C. `theta=pi/2`
D. none of these
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Correct Answer - A
We have,
`{:A^2[(cos 2theta,sin2theta),(-sin2theta,cos2theta)]:}`
`:. A^2=IrArr cos 2theta=1 and sin2theta=0rArr theta=0`.
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