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Consider the complex number

z=6(cos(165^(@))+i sin(165^(@)))". "
Which of the following complex numbers best approximates 
z ?
Choose 1 answer:
(A) 
-5.8-1.6 i
(B) 
-1.6+5.8 i
(C) 
-5.8+1.6 i
(D) 
-1.6-5.8 i

Consider the complex number\newlinez=6(cos(165)+isin(165)) z=6\left(\cos \left(165^{\circ}\right)+i \sin \left(165^{\circ}\right)\right) \text {. } \newlineWhich of the following complex numbers best approximates z z ?\newlineChoose 11 answer:\newline(A) 5.81.6i -5.8-1.6 i \newline(B) 1.6+5.8i -1.6+5.8 i \newline(C) 5.8+1.6i -5.8+1.6 i \newline(D) 1.65.8i -1.6-5.8 i

Full solution

Q. Consider the complex number\newlinez=6(cos(165)+isin(165)) z=6\left(\cos \left(165^{\circ}\right)+i \sin \left(165^{\circ}\right)\right) \text {. } \newlineWhich of the following complex numbers best approximates z z ?\newlineChoose 11 answer:\newline(A) 5.81.6i -5.8-1.6 i \newline(B) 1.6+5.8i -1.6+5.8 i \newline(C) 5.8+1.6i -5.8+1.6 i \newline(D) 1.65.8i -1.6-5.8 i
  1. Convert to rectangular form: Convert the given complex number in polar form to rectangular form using the cosine and sine values.\newlineThe complex number zz is given in polar form as z=6(cos(165°)+isin(165°))z = 6(\cos(165°) + i \sin(165°)). To convert it to rectangular form, we use the definitions of cosine and sine for the given angle.
  2. Calculate cosine and sine: Calculate the cosine and sine of 165°165°. Using the unit circle or trigonometric tables, we find that: cos(165°)0.9659\cos(165°) \approx -0.9659 (since 165°165° is in the second quadrant where cosine is negative) sin(165°)0.2588\sin(165°) \approx 0.2588 (since 165°165° is in the second quadrant where sine is positive)
  3. Multiply by modulus: Multiply the cosine and sine values by the modulus of the complex number.\newlineThe modulus of zz is 66. Therefore, we multiply the cosine and sine values by 66 to get the rectangular form:\newlineReal part: 6×cos(165°)6×(0.9659)5.79546 \times \cos(165°) \approx 6 \times (-0.9659) \approx -5.7954\newlineImaginary part: 6×sin(165°)6×0.25881.55286 \times \sin(165°) \approx 6 \times 0.2588 \approx 1.5528
  4. Round real and imaginary parts: Round the real and imaginary parts to one decimal place to match the answer choices.\newlineReal part rounded: 5.8-5.8\newlineImaginary part rounded: 1.61.6
  5. Form complex number: Form the complex number with the rounded real and imaginary parts.\newlineThe approximate complex number in rectangular form is 5.8+1.6i-5.8 + 1.6i.
  6. Match with answer choices: Match the approximate complex number with the given answer choices.\newlineThe approximate complex number 5.8+1.6i-5.8 + 1.6i matches with choice (C) 5.8+1.6i-5.8 + 1.6i.

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