Chapter 8.3, Problem 41E

To determine

To calculate: To write the complex number in polar form with argument $\theta$ between $0$ and $2\pi$

Answer to Problem 41E

Complex number in polar form is $z=20\left(\cos 2\pi +isin2\pi \right)$

Explanation of Solution

Given information: Complex numbers is $z=-20$

Formula Used:

Complex number is a number that can be expressed in the form of $a+bi$ , where $a$ and $b$ are real numbers

  $z=a+bi$

Polar form of the complex number is given as

  $z=r\left(\cos \theta +isin\theta \right)$

Where,

  $r=\left|z\right|=\sqrt{a^2+b^2}$

  $\tan \theta =\frac{b}{a}$

Calculation:

Complex number is given as

  $z=-20$

Polar form of the complex number is given as

  $z=r\left(\cos \theta +isin\theta \right)----(1)$

Calculating the value of $r$ as follows:

  $r=\left|z\right|=\sqrt{a^2+b^2}$

Substituting the values,

  $\begin{array}{l}r=\sqrt{{\left(-20\right)}^2+0^2}\\ r=\sqrt{400}\\ r=20\end{array}$

Calculating the value of $\theta$ as follows:

  $\tan \theta =\frac{b}{a}$

Substituting the values,

  $\begin{array}{l}\tan \theta =\frac{0}{-20}\\ \theta ={\tan }^{-1}\frac{0}{-20}\end{array}$

Here, solution lies in fourth quadrant

  $\theta =2\pi$

Now, substituting the values of $r=20$ and $\theta =2\pi$ in equation (1) to get the complex number in polar form

  $z=20\left(\cos 2\pi +isin2\pi \right)$

Conclusion:

Hence, complex number in polar form is $z=20\left(\cos 2\pi +isin2\pi \right)$