Q35P - Mathematical Methods in Physical Sciences

Question

Use Problems 27 and 28 to find the following absolute values. If you understand Problems 27 and 28 and equation (5.1), you should be able to do these in your head.

$\mathbf{|}\mathbf{3}{\mathbf{e}}^{\mathbf{5}\mathbf{i}}\mathbf{\times }\mathbf{7}{\mathbf{e}}^{\mathbf{-}\mathbf{2}\mathbf{i}}\mathbf{|}$

Step-by-Step Solution

Answer

The absolute value of the expression $|3{\mathrm{e}}^{5\mathrm{i}}\times 7{\mathrm{e}}^{-2\mathrm{i}}|=21.$ .

Step 1: Given information

The given complex number is $|3{\mathrm{e}}^{5\mathrm{i}}\times 7{\mathrm{e}}^{-2\mathrm{i}}|$  .

Step 2: Definition of complex numbers

If  a and b are real numbers, then a combination of these real numbers with the imaginary number i can be written as:

 

  $\mathbf{z}\mathbf{=}\mathbf{a}\mathbf{+}\mathbf{ib}\mathbf{ }$

 

Here z is the complex number.

Step 3: Use the result concluded in problem 27

Let the complex number$3{\mathrm{e}}^{5\mathrm{i}}\times 7{\mathrm{e}}^{-2\mathrm{i}}$   be z .   

  $$\begin{gathered} \mathrm{z}=\left|21{\mathrm{e}}^{5\mathrm{i}}{\mathrm{e}}^{-2\mathrm{i}}\right| \\ \mathrm{z}=\left|21{\mathrm{e}}^3\mathrm{i}\right| \dots \dots \dots \dots \dots .\left(1\right) \end{gathered}$$               

                                                                                                  

 Use the result concluded in problem 27 as:

 

$$\begin{gathered} \mathrm{R}=\overline{){\mathrm{re}}^{\left(\mathrm{i\theta }\right)}} \\ \mathrm{R}=\mathrm{r} \end{gathered}$$                                                                                            ……………(2)

 

Compare equations (1) and (2) as:

 $R=21.$

 

 Hence the absolute value of the expression $|3{\mathrm{e}}^{5\mathrm{i}}\times 7{\mathrm{e}}^{-2\mathrm{i}}|=21.$ .