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Question -

If z1 and z2 are two complex number suchthat |z1| = |z2| and arg (z1) + arg (z2)= π, then show that 



Answer -

|z1| = |z2|and arg (z1) + arg (z2) = π

Let us assume arg (z1)= θ

arg (z2) =π – θ

We know that in thepolar form, z = |z| (cos θ + i sin θ)

z=|z1| (cos θ + i sin θ) …………. (i)

z=|z2| (cos (π – θ) + i sin (π – θ))

= |z2|(-cos θ + i sin θ)

= – |z2|(cos θ – i sin θ)

Now let us find theconjugate of

= – |z2|(cos θ + i sin θ) …… (ii) (since, |Z2¯¯¯¯¯¯|=|Z2|)

Now,

z1 /= [|z1| (cos θ + i sinθ)] / [-|z2| (cos θ + i sin θ)]

= – |z1| /|z2| [since, |z1| = |z2|]

= -1

When we cross multiplywe get,

z1 = –

Hence proved.

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