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If Z1 and Z2 Are Two Complex Numbers Such that | Z 1 | = | Z 2 | and Arg(Z1) + Arg(Z2) = π Then Show that Z 1 = − ¯ Z 2 .

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Question

If z1 and z2 are two complex numbers such that \[\left| z_1 \right| = \left| z_2 \right|\] and arg(z1) + arg(z2) = \[\pi\] then show that \[z_1 = - \bar{{z_2}}\].

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Solution

Let θbe the arg(z1) and θbe the arg(z2).
It is given that

\[\left| z_1 \right| = \left| z_2 \right|\] and arg(z1) + arg(z2) = \[\pi\].

Since, z1 is a complex number.

\[z_1 = \left| z_1 \right|\left( \cos \theta_1 + i\sin \theta_1 \right)\]

\[ = \left| z_2 \right|\left[ \cos\left( \pi - \theta_2 \right) + i\sin\left( \pi - \theta_2 \right) \right]\]

\[ = \left| z_2 \right|\left[ - \cos\left( \theta_2 \right) + i\sin\left( \theta_2 \right) \right]\]

\[ = - \left| z_2 \right|\left[ \cos\left( \theta_2 \right) - i\sin\left( \theta_2 \right) \right]\]

\[ = - \bar{{z_2}}\]

Hence,  

\[z_1 = - \bar{{z_2}}\].

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Chapter 13: Complex Numbers - Exercise 13.4 [Page 57]

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R.D. Sharma Mathematics [English] Class 11
Chapter 13 Complex Numbers
Exercise 13.4 | Q 4 | Page 57

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