4-1.Complex numbers
easy

બે સંકર સંખ્યા ${z_1}$ અને ${z_2}$ છે અને કોઈ વાસ્તવિક સંખ્યા $a$ અને $b$ માટે; $|(a{z_1} - b{z_2}){|^2} + |(b{z_1} + a{z_2}){|^2} = $

A

$({a^2} + {b^2})(|{z_1}| + |{z_2}|)$

B

$({a^2} + {b^2})(|{z_1}{|^2} + |{z_2}{|^2})$

C

$({a^2} + {b^2})(|{z_1}{|^2} - |{z_2}{|^2})$

D

એકપણ નહીં.

(IIT-1988)

Solution

(b)$|(a{z_1} – b{z_2}){|^2} + |(b{z_1} + a{z_2}){|^2}$
$ = {a^2}|{z_1}{|^2} + {b^2}|{z_2}{|^2} – 2{\mathop{\rm Re}\nolimits} (ab)|{z_1}{\overline z _2}|+ {b^2}|{z_1}{|^2} + $${a^2}|{z_2}{|^2} + 2{\mathop{\rm Re}\nolimits} (ab)|{\overline z _1}{z_2}|$
$ = ({a^2} + {b^2})(|{z_1}{|^2} + |{z_2}{|^2})$

Standard 11
Mathematics

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