The polar form of a complex number is given by , where and , and the complex number .
- (i)
Find in exact polar form in terms of and .
- (ii)
Given that is real and positive, find the possible value(s) of in exact form, leaving your answer(s) in terms of .
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Worked solution
4(i)
1. Find the modulus and argument of the complex number multiplier $\frac{1}{3} - \frac{\sqrt{3}}{3}\text{i}$.
Let .
Since the real part is positive and the imaginary part is negative, the complex number lies in the fourth quadrant.
Thus, .
2. Multiply the complex numbers to express $w$ in exact polar form.
Since , the argument lies within the principal range , so no adjustment is required.
4(ii)
1. Express $z^5$ and $w^*$ in exponential form.
From part (i), .
The complex conjugate is found by negating the argument:
Using standard index laws (De Moivre's Theorem for exponential forms),
2. Find the quotient $\frac{z^5}{w^*}$ in exponential form.
3. Form an equation using the condition that the quotient is real and positive.
For a complex number to be real and positive, its imaginary part is 0 and its real part is positive, which means its argument must be an integer multiple of .
4. Solve for the possible values of $\theta$ within the specified domain.
We are given the domain .
Substituting integer values for :
For ,
For ,
For ,
For , (Reject, as )
For , (Reject, as )
The possible exact values are , , and .
\frac{\pi}{18}, \frac{7\pi}{18}, \frac{13\pi}{18}
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