Answer: cos(-90°) + i sin(-90°).
- A 1(cos 90° + i sin 90°)
- B 1(cos 270° + i sin 270°)
- C 1(cos 180° + i sin 180°)
- D cos(-90°) + i sin(-90°)
Correct answer: D. cos(-90°) + i sin(-90°)
Explanation: z = -i = 0 - 1i. Modulus = 1, arg = -pi/2 = -90 degrees. Polar: cos(-90) + i sin(-90).
A complex number z = a+ib is plotted as a point (or vector from the origin) on the Argand plane, with the real part along the horizontal axis and the imaginary part along the vertical; its modulus |z| is the vector's length, and its argument θ is the angle from the positive real axis.
Concept context
Complex numbers in a+ib form, modulus, argument, polar form, cube roots of unity, and quadratic equations with complex roots
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