Q12P - Mathematical Methods in Physical Sciences

Question

Express the following complex numbers in the $\mathit{x}\mathbf{+}\mathit{i}\mathit{y}$form. Try to visualize each complex number, using sketches as in the examples if necessary. The first twelve problems you should be able to do in your head (and maybe some of the others—try it!) Doing a problem quickly in your head saves time over using a computer. Remember that the point in doing problems like this is to gain skill in manipulating complex expressions, so a good study method is to do the problems by hand and use a computer to check your answers.

 

12. $\mathbf{4}{\mathit{e}}^{\mathbf{-}\mathbf{8}\mathbf{i}\mathbf{\pi }\mathbf{/}\mathbf{3}}$

Step-by-Step Solution

Answer

The complex number in $x+iy$ form is$z=-2-2\sqrt{3}i$.

Step 1: Given information

The Given complex number is$4e^{-8i\mathrm{\pi }/3}$.

Step 2: Definition of Complex Number

The numbers that are presented in the form of $\mathit{a}\mathbf{+}\mathit{i}\mathit{b}$, where, $\mathit{a}\mathbf{,}\mathit{b}$ are real numbers and $\mathbf{\text{'}}\mathit{i}\mathbf{\text{'}}$ is an imaginary number called complex numbers.

Step 3: Finding the general form x + i y

Let the given complex number be$4e^{-8i\mathrm{\pi }/3}$.

Polar form of complex number is $z=r{e}^{\left(\theta \right)}$.

Polar form of complex number is $z=r\left(\cos \left(\theta \right)+i\sin \left(\theta \right)\right)$ …(1)

Compare with given complex number.

$$\begin{gathered} r=4 \\ \theta =\frac{-8\mathrm{\pi i}}{3} \end{gathered}$$

The value of $x,y$ is $\cos \left(\theta \right),\sin \left(\theta \right)$ respectively.

$$\begin{gathered} x=\cos \left(\theta \right) \\ y=\sin \left(\theta \right) \end{gathered}$$

Put the values of $r$ and $\theta$ in the equation $\left(1\right)$.

$$\begin{gathered} 4\left[\cos \left(\frac{-8\mathrm{\pi i}}{3}+4\mathrm{\pi i}\right)+i\sin \left(\frac{-8\mathrm{\pi i}}{3}+4\mathrm{\pi i}\right)\right]=4\cos \left(\frac{-8\mathrm{\pi i}}{3}+4\mathrm{\pi i}\right)+i4\sin \left(\frac{-8\mathrm{\pi i}}{3}+4\mathrm{\pi i}\right) \\ =-2-2\sqrt{3}i \end{gathered}$$

The general form is$-2-2\sqrt{3}i$.

Step 4: Draw the graph of complex number

Plot the complex number$-2-2\sqrt{3}i$.