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If z1, z2 and z3, z4 are two pairs of conjugate complex numbers, then find arg(z1z4) + arg(z2z3). - Mathematics

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Question

If z1, z2 and z3, z4 are two pairs of conjugate complex numbers, then find arg`(z_1/z_4)` + arg`(z_2/z_3)`.

Sum

Solution

Let the polar form of z1 = r1(cosθ1 + isinθ1)

∴ z2 = `barz_1` 

= r1(cosθ1 + isinθ1)

= r1[cos(–θ1) + isin(–θ1)]

Similarly, z3 = r2(cosθ2 + isinθ2)

∴ z4 = `barz_3`

= r2(cosθ2 + isinθ2)

= r2[cos(–θ2) + isin(–θ2)]

arg`(z_1/z_4)` + arg`(z_2/z_3)` = arg(z1) – arg(z4) + arg(z2) – arg(z3)

= θ1 – (–θ2) + (–θ1) – θ2

= θ1 + θ2 – θ1 – θ2

= 0

Hence, arg`(z_1/z_4)` + arg`(z_2/z_3)` = 0.

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Chapter 5: Complex Numbers and Quadratic Equations - Exercise [Page 92]

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NCERT Exemplar Mathematics [English] Class 11
Chapter 5 Complex Numbers and Quadratic Equations
Exercise | Q 18 | Page 92

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