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Find the argument of the complex number 
-1-sqrt3i in the interval 
0 <= theta < 2pi. Express your answer in terms of 
pi.

Find the argument of the complex number 13i -1-\sqrt{3} i in the interval 0θ<2π 0 \leq \theta<2 \pi . Express your answer in terms of π \pi .

Full solution

Q. Find the argument of the complex number 13i -1-\sqrt{3} i in the interval 0θ<2π 0 \leq \theta<2 \pi . Express your answer in terms of π \pi .
  1. Identify Complex Number: To find the argument of a complex number in the form a+bia + bi, where aa is the real part and bb is the imaginary part, we need to calculate the angle θ\theta that the line representing the complex number makes with the positive real axis in the complex plane. The complex number given is 13i-1 - \sqrt{3}i, so a=1a = -1 and b=3b = -\sqrt{3}.
  2. Calculate Argument Formula: The argument of a complex number is given by the arctan(ba)\text{arctan}(\frac{b}{a}) when a>0a > 0. However, when a<0a < 0 and b<0b < 0, as in this case, the complex number lies in the third quadrant of the complex plane. The formula for the argument θ\theta in this case is θ=arctan(ba)+π\theta = \text{arctan}(\frac{b}{a}) + \pi, because we need to account for the additional π\pi radians to reach the third quadrant from the positive real axis.
  3. Calculate arctan(ba)\arctan(\frac{b}{a}): We calculate the arctan(ba)\arctan(\frac{b}{a}) using the values of aa and bb. Here, ba=31\frac{b}{a} = \frac{\sqrt{3}}{1}. The arctan(3)\arctan(\sqrt{3}) is known to be π3\frac{\pi}{3}, because tan(π3)=3\tan(\frac{\pi}{3}) = \sqrt{3}. However, since we are in the third quadrant, we need to add π\pi to this value to get the correct argument.
  4. Add pi for Third Quadrant: Adding π\pi to π/3\pi/3 gives us the argument θ\theta in the third quadrant. So, θ=π/3+π=(1/3)π+(3/3)π=(4/3)π\theta = \pi/3 + \pi = (1/3)\pi + (3/3)\pi = (4/3)\pi.
  5. Check Interval: We check to ensure that our argument is within the specified interval 0θ<2π0 \leq \theta < 2\pi. Since (43)π(\frac{4}{3})\pi is between 00 and 2π2\pi, our answer is within the correct interval.

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