Let A,B,C be three collinear points which are such that AB.AC=1 and the points are represented in the Argand plane by the complex numbers0,z1,z2 respectively. Then
A
z1,z2=1
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B
z1.¯z2=1
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C
|z1||z2|=1
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D
none of these
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Solution
The correct options are Az1.¯z2=1 B|z1||z2|=1 Since the points 0,z1,z2 lie on a same line, arg(z1)=arg(z2) Hence they must lie on a line of the form y=mx Now AB=z1 AC=z2 z1.z2=1 z1=¯¯¯¯¯z2 However z1 and z2 have the same argument. Hence this is only possible if z1 and z2 both are purely real. Therefore z1=¯¯¯¯¯z1 and z2=¯¯¯¯¯z2 Only |z1|=1|z2| Hence z1.¯¯¯¯¯z2=z1.z2=1 And |z1||z2|=1