1.

`z_(1) "the"z_(2) "are two complex numbers such that" |z_(1)| = |z_(2)|`. "and" arg `(z_(1)) + arg (z_(2) = pi," then show that "z_(1) = - barz_(2).`

Answer» Let `z_(1) = r_(1) (costheta_(1) + i sintheta _(1))` and `z_(1) = r_(1)(costheta_(1) + i sintheta _(1)) are two complex numbers.
Given that `|z_(1)| = |z_(2)|`
and `arg (z_(1)) + arg (z_(2)) = pi`
If `|z_(1)|= |z_(2)|`
`rArr r_(1) = r_(2) ...(i)
and if `arg (z_(1)) + arg (z_(2)) = pi`
` rArr theta _(1) + theta_(2) = pi`
`rArr theta ^(1) = pi - theta_(2)`
Now, `z_(1) = r_(1) (costheta_(1) + i sintheta _(1))`
`rArr z_(1) = r_(2) [(cos(pi -theta_(2)) + i sin (pi- theta_(2))]" "[:.r_(1) = r_(2) and theta_(1) = (pi-theta_(2))]`
`rArr `z_(1) = r_(2) (-costheta_(2) + i sin theta_(2))` ltbr. `rArr z_(1) = - r_(2) (costheta_(2) - i sin theta_(2))`
`z_(1) = -[r_(2) (costheta_(2) - i sin theta_(2))]`
`rArr z_(1) = - barz_(2)" "[:. barz = r_(2)(costheta_(2) -i sintheta _(2))]`


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