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Question

Let zr(1r4) be complex numbers such that |zr|=r+1and|30 z1+20 z2+15z3+12 z4|=k|z1z2z3+z2z3z4+z3z4z1+z4z1z2|. Then value of k equals ?

A
|z1z2z3|
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B
|z2z3z4|
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C
|z3z4z1|
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D
|z4z1z2|
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Solution

The correct option is D |z4z1z2|
|z1|=2, |z2|=3, |z3|=4, |z4|=5

|30z1+20z2+15z3+12z4|=k|z1z2z3+z2z3z4+z3z4z1+z4z1z2|

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯|30z1+20z2+15z3+12z4|=k|z1z2z3+z2z3z4+z3z4z1+z4z1z2|

|30¯z1+20¯z2+15¯z3+12¯z4|=k|z1z2z3+z2z3z4+z3z4z1+z4z1z2

z1¯z1=2, z2¯z2=3, z3¯z3=4, z4¯z4=5

601z1+1z2+1z3+1z4=k|z1z2z3+z2z3z4+z3z4z1+z4z1z2|

k=|z4z1z2|

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