Real Part Zw
1. **State the problem:**
We are given two complex numbers in polar form:
$$z = 2 \operatorname{cis} \left(-\frac{\pi}{4}\right)$$
and
$$w = \sqrt{3} \operatorname{cis} \left(\frac{\pi}{6}\right)$$
We need to find the real part of the product $$zw$$, denoted as $$\operatorname{Re}(zw)$$, and express it as a decimal rounded to 3 significant figures.
2. **Recall the formula for multiplication of complex numbers in polar form:**
If $$z = r_1 \operatorname{cis} \theta_1$$ and $$w = r_2 \operatorname{cis} \theta_2$$, then
$$zw = r_1 r_2 \operatorname{cis} (\theta_1 + \theta_2)$$
where $$\operatorname{cis} \theta = \cos \theta + i \sin \theta$$.
3. **Calculate the magnitude and argument of $$zw$$:**
$$r = 2 \times \sqrt{3} = 2\sqrt{3}$$
$$\theta = -\frac{\pi}{4} + \frac{\pi}{6} = -\frac{3\pi}{12} + \frac{2\pi}{12} = -\frac{\pi}{12}$$
4. **Express $$zw$$ in rectangular form:**
$$zw = 2\sqrt{3} \left( \cos \left(-\frac{\pi}{12}\right) + i \sin \left(-\frac{\pi}{12}\right) \right)$$
5. **Find the real part:**
Since $$\cos(-\theta) = \cos \theta$$,
$$\operatorname{Re}(zw) = 2\sqrt{3} \cos \left(\frac{\pi}{12}\right)$$
6. **Calculate $$\cos \left(\frac{\pi}{12}\right)$$:**
Using the half-angle formula or known values,
$$\cos \left(\frac{\pi}{12}\right) = \cos 15^\circ = \frac{\sqrt{6} + \sqrt{2}}{4} \approx 0.9659$$
7. **Calculate the final value:**
$$\operatorname{Re}(zw) = 2 \times 1.732 \times 0.9659 \approx 3.346$$
8. **Round to 3 significant figures:**
$$\boxed{3.35}$$
Thus, the real part of $$zw$$ is approximately 3.35.