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QJEEAdv22Ma4ea5: JEE Advanced 2022 Mathematics - Class 11 JEEAdv22Ma4ea5 Solution: Let denote the determinant of a square matrix . Let be the…

Let ∣M∣|M| denote the determinant of a square matrix MM . Let g:[0,π2]→Rg:\left[0, \frac{\pi}{2}\right] \rightarrow \mathbb{R} be the function defined by

g(θ)=f(θ)−1+f(π2−θ)−1g(\theta)=\sqrt{f(\theta)-1}+\sqrt{f\left(\frac{\pi}{2}-\theta\right)-1}

where

f(θ)=12∣1amp;sin⁡θamp;1−sin⁡θamp;1amp;sin⁡θ−1amp;−sin⁡θamp;1∣+∣sin⁡πamp;cos⁡(θ+π4)amp;tan⁡(θ−π4)sin⁡(θ−π4)amp;−cos⁡π2amp;log⁡e(4π)cot⁡(θ+π4)amp;log⁡e(π4)amp;tan⁡π∣.f(\theta)=\frac{1}{2}\left|\begin{array}{ccc}1 & \sin \theta & 1 \\-\sin \theta & 1 & \sin \theta \\-1 & -\sin \theta & 1\end{array}\right|+\left|\begin{array}{ccc}\sin \pi & \cos \left(\theta+\frac{\pi}{4}\right) & \tan \left(\theta-\frac{\pi}{4}\right) \\\sin \left(\theta-\frac{\pi}{4}\right) & -\cos \frac{\pi}{2} & \log _{e}\left(\frac{4}{\pi}\right) \\\cot \left(\theta+\frac{\pi}{4}\right) & \log _{e}\left(\frac{\pi}{4}\right) & \tan \pi\end{array}\right| .

Let p(x)p(x) be a quadratic polynomial whose roots are the maximum and minimum values of the function g(θ)g(\theta) , and p(2)=2−2p(2)=2-\sqrt{2} . Then, which of the following is/are TRUE ?

Multiple Choice Options

  • A p(3+24)<0p\left(\frac{3+\sqrt{2}}{4}\right)<0
  • B p(1+324)>0p\left(\frac{1+3 \sqrt{2}}{4}\right)>0
  • C p(52−14)>0p\left(\frac{5 \sqrt{2}-1}{4}\right)>0
  • D p(5−24)<0p\left(\frac{5-\sqrt{2}}{4}\right)<0

Step-by-Step Verified Solution

Given,

f(θ)=12∣1amp;sin⁡θamp;1−sin⁡θamp;1amp;sin⁡θ−1amp;−sin⁡θamp;1∣+∣sin⁡πamp;cos⁡(θ+π4)amp;tan⁡(θ−π4)sin⁡(θ−π4)amp;−cos⁡π2amp;log⁡e(4π)cot⁡(θ+π4)amp;log⁡e(π4)amp;tan⁡π∣f(\theta)=\frac{1}{2}\left|\begin{array}{ccc}1 &amp; \sin \theta &amp; 1 \\-\sin \theta &amp; 1 &amp; \sin \theta \\-1 &amp; -\sin \theta &amp; 1\end{array}\right|+\left|\begin{array}{ccc}\sin \pi &amp; \cos \left(\theta+\frac{\pi}{4}\right) &amp; \tan \left(\theta-\frac{\pi}{4}\right) \\\sin \left(\theta-\frac{\pi}{4}\right) &amp; -\cos \frac{\pi}{2} &amp; \log _{e}\left(\frac{4}{\pi}\right) \\\cot \left(\theta+\frac{\pi}{4}\right) &amp; \log _{e}\left(\frac{\pi}{4}\right) &amp; \tan \pi\end{array}\right|

Here cos⁡(θ+π4)=−sin⁡(θ−π4)\cos \left(\theta+\frac{\pi}{4}\right)=-\sin \left(\theta-\frac{\pi}{4}\right)

and tan⁡(θ−π4)=−cot⁡(θ+π4)\tan \left(\theta-\frac{\pi}{4}\right)=-\cot \left(\theta+\frac{\pi}{4}\right)

and log⁡e(4π)=−log⁡e(π4)\log _e\left(\frac{4}{\pi}\right)=-\log _e\left(\frac{\pi}{4}\right)

Also sin⁡π=−cos⁡π2=tan⁡π=0\sin \pi=-\cos \frac{\pi}{2}=\tan \pi=0

⇒\Rightarrow f(θ)=12∣2amp;sin⁡θamp;10amp;1amp;sin⁡θ0amp;−sin⁡θamp;1∣+∣0amp;−sin⁡(θ−π4)amp;tan⁡(θ−π4)sin⁡(θ−π4)amp;0amp;log⁡e(4π)−tan⁡(θ−π4)amp;−log⁡e(4π)amp;0∣f(\theta)=\frac{1}{2}\left|\begin{array}{ccc}2 &amp; \sin \theta &amp; 1 \\0 &amp; 1 &amp; \sin \theta \\0 &amp; -\sin \theta &amp; 1\end{array}\right|+\left|\begin{array}{ccc}0 &amp; -\sin \left(\theta-\frac{\pi}{4}\right) &amp; \tan \left(\theta-\frac{\pi}{4}\right) \\\sin \left(\theta-\frac{\pi}{4}\right) &amp; 0 &amp; \log _{\mathrm{e}}\left(\frac{4}{\pi}\right) \\-\tan \left(\theta-\frac{\pi}{4}\right) &amp; -\log _{\mathrm{e}}\left(\frac{4}{\pi}\right) &amp; 0\end{array}\right|

amp;f(θ)=(1+sin⁡2θ)+0 (skew symmetric) amp;g(θ)=f(θ)−1+f(π2−θ)−1amp;=∣sin⁡θ∣+∣cos⁡θ∣amp;g(θ)∈[1,2] for θ∈[0,π2]\begin{aligned}&amp; f(\theta)=\left(1+\sin ^2 \theta\right)+0 \text { (skew symmetric) } \\\\&amp; g(\theta)=\sqrt{f(\theta)-1}+\sqrt{f\left(\frac{\pi}{2}-\theta\right)-1} \\\\&amp; =|\sin \theta|+|\cos \theta| \quad \\\\&amp; g(\theta) \in[1, \sqrt{2}] \text { for } \theta \in\left[0, \frac{\pi}{2}\right]\end{aligned}

Again let P(x)=k(x−2)(x−1)\mathrm{P}(\mathrm{x})=\mathrm{k}(\mathrm{x}-\sqrt{2})(\mathrm{x}-1)

amp;2−2=k(2−2)(2−1)amp;⇒k=1(P(2)=2−2 given )amp;∴P(x)=(x−2)(x−1)\begin{aligned}&amp; 2-\sqrt{2}=\mathrm{k}(2-\sqrt{2})(2-1) \\\\&amp; \Rightarrow \mathrm{k}=1 \quad(\mathrm{P}(2)=2-\sqrt{2} \text { given }) \\\\&amp; \therefore \mathrm{P}(\mathrm{x})=(\mathrm{x}-\sqrt{2})(\mathrm{x}-1)\end{aligned}

For option (A) P\left(\frac{3+\sqrt{2}}{4}\right)&lt;0 Correct.

For option (B) P\left(\frac{1+3 \sqrt{2}}{4}\right)&lt;0 Incorrect.

For option (C) P\left(\frac{5 \sqrt{2}-1}{4}\right)&gt;0 Correct.

For option (D) P\left(\frac{5-\sqrt{2}}{4}\right)&gt;0 Incorrect.

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