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Find the argument of the complex number 
-3sqrt3+9i in the interval 
0 <= theta < 2pi. Express your answer in terms of 
pi.
Answer:

Find the argument of the complex number 33+9i -3 \sqrt{3}+9 i in the interval 0 \leq \theta<2 \pi . Express your answer in terms of π \pi .\newlineAnswer:

Full solution

Q. Find the argument of the complex number 33+9i -3 \sqrt{3}+9 i in the interval 0θ<2π 0 \leq \theta<2 \pi . Express your answer in terms of π \pi .\newlineAnswer:
  1. Identify parts of 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 use the formula θ=arctan(ba)\theta = \text{arctan}(\frac{b}{a}). However, since the arctan\text{arctan} function only gives values from π2-\frac{\pi}{2} to π2\frac{\pi}{2}, we need to consider the quadrant in which the complex number lies to find the correct argument in the interval 0 \leq \theta < 2\pi.
  2. Calculate principal value of argument: First, identify the real part aa and the imaginary part bb of the complex number 33+9i-3\sqrt{3} + 9i. Here, a=33a = -3\sqrt{3} and b=9b = 9.
  3. Consider quadrant for correct argument: Next, calculate the arctan(ba)\arctan(\frac{b}{a}) to find the principal value of the argument. However, since aa is negative and bb is positive, the complex number lies in the second quadrant. In the second quadrant, the argument θ\theta is πarctan(ba)\pi - \arctan(\left|\frac{b}{a}\right|).
  4. Compute absolute value of b/ab/a: Compute the absolute value of b/ab/a: ba=9(33)=33=3|\frac{b}{a}| = |\frac{9}{(-3\sqrt{3})}| = |\frac{-3}{\sqrt{3}}| = |-\sqrt{3}|.
  5. Calculate arctan(3)\arctan(-\sqrt{3}): Now, calculate arctan(3)\arctan(\lvert-\sqrt{3}\rvert). Since arctan(3)\arctan(\sqrt{3}) is known to be π3\frac{\pi}{3}, arctan(3)\arctan(-\sqrt{3}) will also be π3-\frac{\pi}{3}.
  6. Determine argument in second quadrant: Since the complex number is in the second quadrant, the argument θ\theta is π(π/3)\pi - (-\pi/3), which simplifies to π+π/3\pi + \pi/3.
  7. Find argument in interval 00 to 2π2\pi: Add π\pi and π/3\pi/3 to find the argument of the complex number in the interval 0 \leq \theta < 2\pi: θ=π+π/3=(3π/3)+(π/3)=4π/3\theta = \pi + \pi/3 = (3\pi/3) + (\pi/3) = 4\pi/3.

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