Answer: k less than or equal to 9.
- A k > 9, obtained by reversing the discriminant inequality
- B k less than or equal to 9
- C k < 0, requiring the leading coefficient to be negative
- D k = 9 only, taken from setting the discriminant to zero
Correct answer: B. k less than or equal to 9
Explanation: D = 36 - 4k >= 0. 4k <= 36. k <= 9. Also k cannot be 0 (then not quadratic). k <= 9, k not 0.
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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