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If [tex]z_1 = 2 \operatorname{cis} 120^{\circ}[/tex], [tex]z_2 = 4 \operatorname{cis} 30^{\circ}[/tex], and [tex]\frac{z_1}{z_2} = a + b i[/tex], then [tex]a = \qquad[/tex] and [tex]b = \square[/tex]


Sagot :

To find the values of [tex]\(a\)[/tex] and [tex]\(b\)[/tex] given [tex]\(z_1=2 \operatorname{cis} 120^{\circ}\)[/tex] and [tex]\(z_2=4 \operatorname{cis} 30^{\circ}\)[/tex], we need to divide these two complex numbers in polar form and then convert the result to rectangular form.

### Step-by-Step Solution

1. Divide the Moduli:
[tex]\[ \text{Modulus of } \frac{z_1}{z_2} = \frac{\text{Modulus of } z_1}{\text{Modulus of } z_2} = \frac{2}{4} = \frac{1}{2} \][/tex]

2. Subtract the Arguments:
[tex]\[ \text{Argument of } \frac{z_1}{z_2} = \text{Argument of } z_1 - \text{Argument of } z_2 = 120^{\circ} - 30^{\circ} = 90^{\circ} \][/tex]

3. Convert the Argument from Degrees to Radians:
[tex]\[ 90^{\circ} = \frac{\pi}{2} \text{ radians} \][/tex]

4. Calculate the Rectangular Form:
Given the polar form [tex]\(\frac{z_1}{z_2} = \frac{1}{2} \operatorname{cis} 90^{\circ}\)[/tex], we convert this to rectangular form using the cosine and sine functions:
[tex]\[ \frac{1}{2} \operatorname{cis} 90^{\circ} = \frac{1}{2} (\cos 90^{\circ} + i \sin 90^{\circ}) \][/tex]
Using the values of cosine and sine at [tex]\(90^{\circ}\)[/tex]:
[tex]\[ \cos 90^{\circ} = 0 \quad \text{and} \quad \sin 90^{\circ} = 1 \][/tex]

5. Substitute and Simplify:
[tex]\[ \frac{1}{2} (0 + i \cdot 1) = \frac{1}{2} (0 + i) = 0 + \frac{1}{2}i = 0 + 0.5i \][/tex]

Thus, the values of [tex]\(a\)[/tex] and [tex]\(b\)[/tex] are:
[tex]\[ a = 0 \][/tex]
[tex]\[ b = 0.5 \][/tex]

So the complete answer is:

If [tex]\(z_1=2 \operatorname{cis} 120^{\circ}, z_2=4 \operatorname{cis} 30^{\circ}\)[/tex], and [tex]\(\frac{z_1}{z_2}=a+b i\)[/tex], then [tex]\(a=0\)[/tex] and [tex]\(b=0.5\)[/tex].