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Q.

Let M=sin4θ−1−sin2θ1+cos2θcos4θ=αI+βM−1 , Where α=αθ  and β=βθ  are real numbers, and I is the 2×2 identity matrix. If α*  is the minimum of the set αθ:θ∈[0,2π)  and β*   is the minimum of the set βθ:θ∈[0,2π). Then the value of α*+β*  is

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a

−2916

b

−3716

c

−3116

d

−1716

answer is A.

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Detailed Solution

M=sin4θ-1-sin2θ1+cos2θcos4θ=αI+βM-1 Where α=α(θ) and β=β(θ) are real numbers |M|=(sinθcosθ)4+1+sin2θ1+cos2θ=2+sin2θcos2θ+sin4θcos4θ since M=αI+βM-1sin4θ-1+sin2θ1+cos2θcos4θ=α00α+β|M|cos4θ1+sin2θ-1-cos2θsin4θ Comparing on both side sin4θ=α+β|M|cos4θ-1-sin2θ=β|M|1+sin2θ⇒β=-|M| =-2+sin2θcos2θ+sin4θcos4θ  therefore sin4θ=α-cos4θ ⇒α=αθ=sin4θ+cos4θ=1-2sin2θcos2θ=1-12sin22θα*= minimum of α(θ)=1-121=12now β* =Minimum of βθ=-2+sin2θcos2θ+sin4θcos4θ=-sin2θcos2θ+122+74=-14sin22θ+122+74β*=-14+122+74=-3716  when θ=nπ+π4α*+β*=-3716+12=-37+816=-2916
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