Answer: 5.
- A 3
- B 4
- C 5
- D 6
Correct answer: C. 5
Explanation: (2+i)(2-i) = 2<sup>2</sup> + 1<sup>2</sup> = 4 + 1 = 5.
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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