The complex number \({{\left( \frac{2+i}{3-i} \right)}^{2}}\) is

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ESE Electrical 2019 Official Paper
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  1. \(\frac{1}{2}\left( \cos \frac{\pi }{4}+i\sin \frac{\pi }{4} \right)\)
  2. \(\frac{1}{2}\left( \cos \frac{\pi }{2}+i\sin \frac{\pi }{2} \right)\)
  3. \(\frac{1}{2}~(\cos \pi +i\sin \pi)\)
  4. \(\frac{1}{2}\left( \cos \frac{\pi }{6}+i\sin \frac{\pi }{6} \right)\)

Answer (Detailed Solution Below)

Option 2 : \(\frac{1}{2}\left( \cos \frac{\pi }{2}+i\sin \frac{\pi }{2} \right)\)
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Detailed Solution

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Given complex no. \({{\left( \frac{2+i}{3-i} \right)}^{2}}\)

\(z={{\left( \frac{2+i}{3-i} \right)}^{2}}=\frac{4-1+4i}{9-1-6i}=\frac{3+4i}{8-6i}\)

Rationalize the above expression

\(z=\frac{\left( 3+4i \right)}{\left( 8-6i \right)}\frac{\left( 8+6i \right)}{\left( 8+6i \right)}=\frac{\left( 24+32i+18i-24 \right)}{64+36}=\frac{50i}{100}=\frac{i}{2}\)

\(\Rightarrow z=\frac{i}{2}=\frac{1}{2}~\left[ \cos \frac{\pi }{2}+i\sin \frac{\pi }{2} \right]\)
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