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Let \({z}_{1},{z}_{2}\text{and }{z}_{3}\) be three complex numbers on the circle \(|z|=1\text{ with }\arg \left({z}_{1}\…

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Let \({z}_{1},{z}_{2}\text{and }{z}_{3}\) be three complex numbers on the circle \(|z|=1\text{ with }\arg \left({z}_{1}\right)=\frac{-\pi }{4},\arg \left({z}_{2}\right)=0\) and \(\text{ }\arg \left({z}_{3}\right)=\frac{\pi }{4}.\) If \({\left|{\mathrm{z}}_{1}{\overset{¯}{\mathrm{z}}}_{2}+{\mathrm{z}}_{2}{\overset{¯}{\mathrm{z}}}_{3}+{\mathrm{z}}_{3}{\overset{¯}{\mathrm{z}}}_{1}\right|}^{2}=\alpha +\beta \sqrt{2},\alpha ,\beta \in \mathrm{Z}\) then the value of \({\alpha }^{2}+{\beta }^{2}\) is

[JEE Main 2025, 22 Jan (Shift 1)]

a

24

b

41

c

31

d

29

✓ Correct answer: d)

29

Explanation

\(\text{Given,}\\ {z}_{1}={e}^{-i\pi /4},{z}_{2}=1,{z}_{3}={e}^{i\pi /4}\\ \text{Now,}\\ {\left|{z}_{1}{\overset{¯}{z}}_{2}+{z}_{2}{\overset{¯}{z}}_{3}+{z}_{3}{\overset{¯}{z}}_{1}\right|}^{2}\\ ={\left|{e}^{-i\frac{\pi }{4}}\times 1+1\times {e}^{-i\frac{\pi }{4}}+{e}^{i\frac{\pi }{4}}\times {e}^{i\frac{\pi }{4}}\right|}^{2}\\ ={\left|{e}^{-i\frac{\pi }{4}}+{e}^{-i\frac{\pi }{4}}+{e}^{i\frac{\pi }{2}}\right|}^{2}\\ ={\left|2\left(\cos \frac{\pi }{4}-i\sin \frac{\pi }{4}\right)+\cos \frac{\pi }{2}+i\sin \frac{\pi }{2}\right|}^{2}\\ =|\sqrt{2}-\sqrt{2}\mathrm{i}+\mathrm{i}{|}^{2}\\ =(\sqrt{2}{)}^{2}+(1-\sqrt{2}{)}^{2}\\ =5-2\sqrt{2}\\ \alpha =5,\beta =-2\\ \Rightarrow {\alpha }^{2}+{\beta }^{2}=29\)

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