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Mathematics

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Here's a step-by-step solution to the complex number problem:

Part a· 8 steps

Express z1z_1 and z2z_2 in the form r(cos⁡θ+isin⁡θ)r(\cos\theta + i\sin\theta)

For a complex number z=x+yiz = x + yi, its polar form is z=r(cos⁡θ+isin⁡θ)z = r(\cos\theta + i\sin\theta), where r=x2+y2r = \sqrt{x^2 + y^2} and θ=arctan⁡(yx)\theta = \arctan\left(\frac{y}{x}\right) adjusted for the correct quadrant, such that −π<θ≤π-\pi < \theta \le \pi.

For z1=1+3iz_1 = 1 + \sqrt{3}i:

  1. Identify the real and imaginary parts.

    x1=1x_1 = 1, y1=3y_1 = \sqrt{3}.

  2. Calculate the modulus r1r_1.

    r1=x12+y12=12+(3)2=1+3=4=2r_1 = \sqrt{x_1^2 + y_1^2} = \sqrt{1^2 + (\sqrt{3})^2} = \sqrt{1 + 3} = \sqrt{4} = 2
  3. Calculate the argument θ1\theta_1.

    Since x1>0x_1 > 0 and y1>0y_1 > 0, θ1\theta_1 is in the first quadrant.

    tan⁡θ1=y1x1=31=3\tan\theta_1 = \frac{y_1}{x_1} = \frac{\sqrt{3}}{1} = \sqrt{3} θ1=arctan⁡(3)=π3\theta_1 = \arctan(\sqrt{3}) = \frac{\pi}{3}

    This value is in the range (−π,π](-\pi, \pi].

  4. Write z1z_1 in polar form.

    z1=2(cos⁡π3+isin⁡π3)z_1 = 2\left(\cos\frac{\pi}{3} + i\sin\frac{\pi}{3}\right)

    For z2=−1−iz_2 = -1 - i:

  5. Identify the real and imaginary parts.

    x2=−1x_2 = -1, y2=−1y_2 = -1.

  6. Calculate the modulus r2r_2.

    r2=x22+y22=(−1)2+(−1)2=1+1=2r_2 = \sqrt{x_2^2 + y_2^2} = \sqrt{(-1)^2 + (-1)^2} = \sqrt{1 + 1} = \sqrt{2}
  7. Calculate the argument θ2\theta_2.

    Since x2<0x_2 < 0 and y2<0y_2 < 0, θ2\theta_2 is in the third quadrant.

    tan⁡θ2=y2x2=−1−1=1\tan\theta_2 = \frac{y_2}{x_2} = \frac{-1}{-1} = 1

    The reference angle is π4\frac{\pi}{4}. For the third quadrant, θ2=−(π−π4)=−3π4\theta_2 = -\left(\pi - \frac{\pi}{4}\right) = -\frac{3\pi}{4}.
    This value is in the range (−π,π](-\pi, \pi].

  8. Write z2z_2 in polar form.

    z2=2(cos⁡(−3π4)+isin⁡(−3π4))z_2 = \sqrt{2}\left(\cos\left(-\frac{3\pi}{4}\right) + i\sin\left(-\frac{3\pi}{4}\right)\right)

Part b· 3 steps

Evaluate ∣z1z2∣3\left|\frac{z_1}{z_2}\right|^3 and arg⁡(z1z2)3\arg\left(\frac{z_1}{z_2}\right)^3

  1. Find the polar form of z1z2\frac{z_1}{z_2}.

    If z1=r1(cos⁡θ1+isin⁡θ1)z_1 = r_1(\cos\theta_1 + i\sin\theta_1) and z2=r2(cos⁡θ2+isin⁡θ2)z_2 = r_2(\cos\theta_2 + i\sin\theta_2), then

    z1z2=r1r2(cos⁡(θ1−θ2)+isin⁡(θ1−θ2))\frac{z_1}{z_2} = \frac{r_1}{r_2}(\cos(\theta_1 - \theta_2) + i\sin(\theta_1 - \theta_2))

    Substitute the values from part a):

    r1r2=22=2\frac{r_1}{r_2} = \frac{2}{\sqrt{2}} = \sqrt{2} θ1−θ2=π3−(−3π4)=π3+3π4=4π+9π12=13π12\theta_1 - \theta_2 = \frac{\pi}{3} - \left(-\frac{3\pi}{4}\right) = \frac{\pi}{3} + \frac{3\pi}{4} = \frac{4\pi + 9\pi}{12} = \frac{13\pi}{12}

    So,

    z1z2=2(cos⁡(13π12)+isin⁡(13π12))\frac{z_1}{z_2} = \sqrt{2}\left(\cos\left(\frac{13\pi}{12}\right) + i\sin\left(\frac{13\pi}{12}\right)\right)
  2. Evaluate ∣z1z2∣3\left|\frac{z_1}{z_2}\right|^3.

    Using De Moivre's Theorem, if Z=r(cos⁡θ+isin⁡θ)Z = r(\cos\theta + i\sin\theta), then ∣Zn∣=rn|Z^n| = r^n.
    Here, Z=z1z2Z = \frac{z_1}{z_2}, so r=2r = \sqrt{2} and n=3n=3.

    ∣z1z2∣3=(2)3=22\left|\frac{z_1}{z_2}\right|^3 = (\sqrt{2})^3 = 2\sqrt{2}
  3. Evaluate arg⁡(z1z2)3\arg\left(\frac{z_1}{z_2}\right)^3.

    Using De Moivre's Theorem, arg⁡(Zn)=nθ\arg(Z^n) = n\theta.
    Here, θ=13π12\theta = \frac{13\pi}{12} and n=3n=3.

    arg⁡(z1z2)3=3×13π12=13π4\arg\left(\frac{z_1}{z_2}\right)^3 = 3 \times \frac{13\pi}{12} = \frac{13\pi}{4}

    The argument must be in the range (−π,π](-\pi, \pi]. We adjust 13π4\frac{13\pi}{4} by subtracting multiples of 2π2\pi:

    13π4−2π=13π−8π4=5π4\frac{13\pi}{4} - 2\pi = \frac{13\pi - 8\pi}{4} = \frac{5\pi}{4}

    Since 5π4>π\frac{5\pi}{4} > \pi, we subtract 2π2\pi again:

    5π4−2π=5π−8π4=−3π4\frac{5\pi}{4} - 2\pi = \frac{5\pi - 8\pi}{4} = -\frac{3\pi}{4}

    This value is in the range $(-\pi, \pi

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