Find three cube roots for the following complex number. Leave your answers in trigonometric form. (Enter your answers from smallest to largest angle measure.)125i
Question
Find three cube roots for the following complex number. Leave your answers in trigonometric form. (Enter your answers from smallest to largest angle measure.)125i
Solution
To find the cube roots of a complex number, we first need to convert the complex number into its trigonometric form. The trigonometric form of a complex number is r(cos θ + i sin θ), where r is the magnitude of the complex number and θ is the angle it makes with the positive x-axis.
Step 1: Convert the complex number into trigonometric form The given complex number is 125i, which can be written as 0 + 125i. This corresponds to a point on the complex plane with x-coordinate 0 and y-coordinate 125. The magnitude r of this complex number is √(0² + 125²) = 125. The angle θ it makes with the positive x-axis can be found using the formula θ = atan2(y, x) = atan2(125, 0) = π/2. Therefore, the trigonometric form of the complex number is 125(cos π/2 + i sin π/2).
Step 2: Find the cube roots The cube roots of a complex number r(cos θ + i sin θ) are given by the formula r^(1/3)[cos((θ + 2πk)/3) + i sin((θ + 2πk)/3)], where k = 0, 1, 2. Substituting r = 125 and θ = π/2 into this formula gives the three cube roots:
- 125^(1/3)[cos((π/2 + 2π0)/3) + i sin((π/2 + 2π0)/3)] = 5(cos π/6 + i sin π/6)
- 125^(1/3)[cos((π/2 + 2π1)/3) + i sin((π/2 + 2π1)/3)] = 5(cos 5π/6 + i sin 5π/6)
- 125^(1/3)[cos((π/2 + 2π2)/3) + i sin((π/2 + 2π2)/3)] = 5(cos 3π/2 + i sin 3π/2)
So, the three cube roots of 125i are 5(cos π/6 + i sin π/6), 5(cos 5π/6 + i sin 5π/6), and 5(cos 3π/2 + i sin 3π/2).
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