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Consider the complex number

z=8(cos(240^(@))+i sin(240^(@)))". "
Which of the following complex numbers best approximates 
z ?
Choose 1 answer:
(A) 
6.9-4i
(B) 
-6.9-4i
(C) 
-4-6.9 i
(D) 
4-6.9 i

Consider the complex number z=8(cos(240)+isin(240)) z=8\left(\cos \left(240^{\circ}\right)+i \sin \left(240^{\circ}\right)\right) \text {. } \newlineWhich of the following complex numbers best approximates z z ?\newlineChoose 11 answer:\newline(A) 6.94i 6.9-4 i \newline(B) 6.94i -6.9-4 i \newline(C) 46.9i -4-6.9 i \newline(D) 46.9i 4-6.9 i

Full solution

Q. Consider the complex number z=8(cos(240)+isin(240)) z=8\left(\cos \left(240^{\circ}\right)+i \sin \left(240^{\circ}\right)\right) \text {. } \newlineWhich of the following complex numbers best approximates z z ?\newlineChoose 11 answer:\newline(A) 6.94i 6.9-4 i \newline(B) 6.94i -6.9-4 i \newline(C) 46.9i -4-6.9 i \newline(D) 46.9i 4-6.9 i
  1. Convert to trigonometric form: Convert the given complex number in trigonometric form to standard form.\newlineWe have z=8(cos(240°)+isin(240°))z = 8(\cos(240°) + i \sin(240°)). To convert this to standard form, we need to evaluate the cosine and sine of 240°240°.
  2. Calculate cosine and sine: Calculate the cosine and sine of 240°240°. The angle 240°240° is in the third quadrant, where cosine is negative and sine is also negative. We can use the reference angle of 240°180°=60°240° - 180° = 60° to find the values. cos(240°)=cos(60°)=12\cos(240°) = -\cos(60°) = -\frac{1}{2} sin(240°)=sin(60°)=32\sin(240°) = -\sin(60°) = -\frac{\sqrt{3}}{2}
  3. Substitute values into complex number: Substitute the values of cosine and sine into the complex number. \newlinez=8(12+i(32))z = 8(-\frac{1}{2} + i(-\frac{\sqrt{3}}{2}))\newlinez=8×12+8×i(32)z = 8 \times -\frac{1}{2} + 8 \times i(-\frac{\sqrt{3}}{2})\newlinez=44i3z = -4 - 4i\sqrt{3}
  4. Approximate imaginary part: Approximate the value of 3\sqrt{3} to find the imaginary part of zz.3\sqrt{3} is approximately 1.7321.732. So, the imaginary part of zz is:4i34i×1.7326.928i-4i\sqrt{3} \approx -4i \times 1.732 \approx -6.928i
  5. Write in standard form: Write the complex number in standard form with the approximated values. z46.928iz \approx -4 - 6.928i
  6. Compare with options: Compare the approximated complex number with the given options.\newlineThe approximated complex number is 46.928i-4 - 6.928i. The option that best matches this number is (C) 46.9i-4 - 6.9i.

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