Do not use a calculator in answering this question. The complex numbers zz and ww satisfy the following equations. w+z∗=−2+4iw+z^{*}=-2+4i z+2=3iwz+2=3iw Find zz and ww, giving your answers in the form a+iba+ib, where aa and bb are real numbers.

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Worked solution

2

1. Express $w$ from the first equation and substitute it into the second equation.

From the first equation, express ww:
w=−2+4i−z∗w = -2 + 4i - z^*

Substitute this expression for ww into the second equation:
z+2=3i(−2+4i−z∗)z + 2 = 3i(-2 + 4i - z^*)
z+2=−6i+12i2−3iz∗z + 2 = -6i + 12i^2 - 3iz^*
z+3iz∗=−14−6iz + 3iz^* = -14 - 6i

2. Substitute the Cartesian form $z = a + ib$ to separate the real and imaginary parts.

Let z=a+ibz = a + ib, then the conjugate is z∗=a−ibz^* = a - ib.
Substitute into the equation:
(a+ib)+3i(a−ib)=−14−6i(a + ib) + 3i(a - ib) = -14 - 6i
a+ib+3ai−3i2b=−14−6ia + ib + 3ai - 3i^2 b = -14 - 6i
a+ib+3ai+3b=−14−6ia + ib + 3ai + 3b = -14 - 6i
(a+3b)+i(3a+b)=−14−6i(a + 3b) + i(3a + b) = -14 - 6i

3. Equate real and imaginary parts and solve the resulting simultaneous equations.

Equating real and imaginary parts gives a system of equations:
a+3b=−14— (1)a + 3b = -14 \quad \text{--- (1)}
3a+b=−6— (2)3a + b = -6 \quad \text{--- (2)}

From (2), b=−3a−6b = -3a - 6. Substitute this into (1):
a+3(−3a−6)=−14a + 3(-3a - 6) = -14
a−9a−18=−14a - 9a - 18 = -14
−8a=4  ⟹  a=−12-8a = 4 \implies a = -\frac{1}{2}

Substitute aa back to find bb:
b=−3(−12)−6=−92b = -3\left(-\frac{1}{2}\right) - 6 = -\frac{9}{2}

So, z=−12−92iz = -\frac{1}{2} - \frac{9}{2}i.

4. Find $w$ using the previously found value of $z^*$.

Since z=−12−92iz = -\frac{1}{2} - \frac{9}{2}i, its conjugate is z∗=−12+92iz^* = -\frac{1}{2} + \frac{9}{2}i.
Substitute z∗z^* back into the expression for ww:
w=−2+4i−(−12+92i)w = -2 + 4i - \left(-\frac{1}{2} + \frac{9}{2}i\right)
w=(−2+12)+i(4−92)w = \left(-2 + \frac{1}{2}\right) + i\left(4 - \frac{9}{2}\right)
w=−32−12iw = -\frac{3}{2} - \frac{1}{2}i

Answer

z=−12−92iz = -\frac{1}{2} - \frac{9}{2}i and w=−32−12iw = -\frac{3}{2} - \frac{1}{2}i

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