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z=-2+8i
Find the angle 
theta (in radians) that 
z makes in the complex plane. Round your answer, if necessary, to the nearest thousandth. Express 
theta between 
-pi and 
pi.

theta=

z=2+8i z=-2+8 i \newlineFind the angle θ \theta (in radians) that z z makes in the complex plane. Round your answer, if necessary, to the nearest thousandth. Express θ \theta between π -\pi and π \pi .\newlineθ= \theta=

Full solution

Q. z=2+8i z=-2+8 i \newlineFind the angle θ \theta (in radians) that z z makes in the complex plane. Round your answer, if necessary, to the nearest thousandth. Express θ \theta between π -\pi and π \pi .\newlineθ= \theta=
  1. Identify Real and Imaginary Parts: To find the angle θ\theta that the complex number z=2+8iz = -2 + 8i makes with the positive real axis in the complex plane, we need to calculate the argument of zz. The argument of a complex number is the angle formed by the radius (line from the origin to the point) and the positive x-axis. The argument can be found using the arctan\text{arctan} function, which is the inverse of the tangent function. The formula to find the argument of a complex number a+bia + bi is θ=arctan(b/a)\theta = \text{arctan}(b/a), where aa is the real part and bb is the imaginary part of the complex number.
  2. Calculate Argument using Arctan: First, we identify the real part aa and the imaginary part bb of the complex number z=2+8iz = -2 + 8i. Here, a=2a = -2 and b=8b = 8.
  3. Determine Quadrant and Adjust Angle: Next, we calculate the argument θ\theta using the arctan function: θ=arctan(b/a)=arctan(8/(2))=arctan(4)\theta = \text{arctan}(b/a) = \text{arctan}(8/(-2)) = \text{arctan}(-4). Since the complex number is in the second quadrant (because the real part is negative and the imaginary part is positive), the angle should be in the range (π/2,π)(\pi/2, \pi).
  4. Calculate Final Angle: Using a calculator, we find that arctan(4)1.3258\arctan(-4) \approx -1.3258 radians. However, since the angle is in the second quadrant, we need to add π\pi to this value to get the angle in the correct range. Therefore, θ=1.3258+π\theta = -1.3258 + \pi.
  5. Verify Angle Range: Calculating the value of θ\theta, we get θ1.3258+3.14161.8158\theta \approx -1.3258 + 3.1416 \approx 1.8158 radians.
  6. Verify Angle Range: Calculating the value of θ\theta, we get θ1.3258+3.14161.8158\theta \approx -1.3258 + 3.1416 \approx 1.8158 radians.We check to make sure that our final answer is within the range π-\pi to π\pi. Since 1.81581.8158 is between π-\pi and π\pi, our answer is in the correct range.

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