For any two complex number z1,z2 and any two real numbers a and b, |az1−bz2|2+|bz1+az2|2=
A
(a+b)(|z1|2+|z2|2)
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B
(a2+b2)(|z1|2+|z2|2)
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C
(a2+b2)(|z1|+|z2|)
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D
2(a+b)(|z1|2+|z2|2)
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Solution
The correct option is B(a2+b2)(|z1|2+|z2|2) We know that, [|z1−z2|2=|z1|2+|z2|2−2Re(z1¯¯¯¯¯z2)] and [|z1+z2|2=|z1|2+|z2|2+2Re(z1¯¯¯¯¯z2)] ∴|az1−bz2|2+|bz1+az2|2=a2|z1|2+b2|z2|−2Re(abz1¯¯¯¯¯z2)+b2|z1|2+a2|z2|+2Re(abz1¯¯¯¯¯z2) =|z1|2(a2+b2)+|z2|2(a2+b2) =(a2+b2)(|z1|2+|z2|2)