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Question 12 — JEE Main 04 April 2025 S Ii

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  • #11769
    Om Sharma
    Keymaster

    Let the product of $\omega_{1}=(8+\mathrm{i}) \sin \theta+(7+4 \mathrm{i}) \cos \theta$ and $\omega_{2}=(1+8 \mathrm{i}) \sin \theta+(4+7 \mathrm{i}) \cos \theta$ be $\alpha+\mathrm{i} \beta, \mathrm{i}=\sqrt{-1}$. Let p and q be the maximum and the minimum values of $\alpha+\beta$ respectively. Then $\mathrm{p}+\mathrm{q}$ is equal to [JEE Main 04 April 2025 S II]
    (A) 130
    (B) 160
    (C) 150
    (D) 140

    #11770
    Om Sharma
    Keymaster

    Solution

    $\omega_{1}=(8 \sin \theta+7 \cos \theta)+\mathrm{i}(\sin \theta+4 \cos \theta) ; \omega_{2}=(\sin \theta+4 \cos \theta)+\mathrm{i}(8 \sin \theta+7 \cos \theta)$

    \[ \begin{aligned} & \omega_{1} \omega_{2}=(8 \sin \theta+7 \cos \theta)(\sin \theta+4 \cos \theta)+\mathrm{i}^{2}(\sin \theta+4 \cos \theta)(8 \sin \theta+7 \cos \theta)+\mathrm{i}\left[(\sin \theta+4 \cos \theta)^{2}+(8 \sin \theta+7 \cos \theta)^{2}\right] \\ & \omega_{1} \omega_{2}=0+\mathrm{i}\left(65 \sin ^{2} \theta+120 \sin \theta \cos \theta+65 \cos ^{2} \theta\right) \Rightarrow \omega_{1} \omega_{2}=0+\mathrm{i}(65+60 \sin 2 \theta)=\alpha+\mathrm{i} \beta \therefore \alpha+\beta=0+65+60 \sin 2 \theta \end{aligned} \]

    We know that $-1 \leq \sin 2 \theta \leq 1 \Rightarrow \mathrm{p}=\alpha+\left.\beta\right|_{\text {max }}=65+60=125 ; \mathrm{q}=\alpha+\left.\beta\right|_{\text {min }}=65-60=5 \Rightarrow \mathrm{p}+\mathrm{q}=125+5=130$

    #11771
    Om Sharma
    Keymaster

    Answer

    A

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