Q. Find the argument of the complex number −1−3i in the interval 0≤θ<2π. Express your answer in terms of π.
Identify Complex Number: To find the argument of a complex number in the form a+bi, where a is the real part and b is the imaginary part, we need to calculate the angle θ that the line representing the complex number makes with the positive real axis in the complex plane. The complex number given is −1−3i, so a=−1 and b=−3.
Calculate Argument Formula: The argument of a complex number is given by the arctan(ab) when a > 0. However, when a < 0 and b < 0, as in this case, the complex number lies in the third quadrant of the complex plane. The formula for the argument θ in this case is θ=arctan(ab)+π, because we need to account for the additional π radians to reach the third quadrant from the positive real axis.
Calculate arctan(ab): We calculate the arctan(ab) using the values of a and b. Here, ab=13. The arctan(3) is known to be 3π, because tan(3π)=3. However, since we are in the third quadrant, we need to add π to this value to get the correct argument.
Add pi for Third Quadrant: Adding π to π/3 gives us the argument θ in the third quadrant. So, θ=π/3+π=(1/3)π+(3/3)π=(4/3)π.
Check Interval: We check to ensure that our argument is within the specified interval 0 \leq \theta < 2\pi. Since (34)π is between 0 and 2π, our answer is within the correct interval.
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