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4-1.Complex numbers
normal
If $z_1$ and $z_2$ are two unimodular complex numbers that satisfy $z_1^2 + z_2^2 = 5,$ then ${\left( {{z_1} - {{\bar z}_1}} \right)^2} + {\left( {{z_2} - {{\bar z}_2}} \right)^2}$ is equal to -
A
$6$
B
$5$
C
$9$
D
$10$
Solution
$\left|Z_{1}\right|=1,\left|Z_{2}\right|=1$
$Z_{1}^{2}+Z_{2}^{2}=5$
so $\bar{Z}_{1}^{2}+\bar{Z}_{2}^{2}=5$
$\left(Z_{1}-\bar{Z}_{1}\right)^{2}+\left(Z_{2}-\bar{Z}_{2}\right)^{2}$
$=Z_{1}^{2}+Z_{2}^{2}+\bar{Z}_{1}^{2}+\bar{Z}_{2}^{2}-2\left|Z_{1}\right|^{2}-2\left|Z_{2}\right|^{2}$
$10-4=6$
Standard 11
Mathematics