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CA Foundation · Quantitative Aptitude · Equations

For what positive value of k does the equation x² + kx + 16 = 0 have two equal roots?

Equal roots occur when the discriminant of the quadratic is zero. For this equation that means k² − 64 = 0, so k² = 64 and k = ±8. Because the question asks for the positive value, the answer is 8, not 64.

  1. A4
  2. B8Correct
  3. C16
  4. D64

Explanation

Equal roots require the discriminant b² − 4ac to be zero. Here k² − 4(1)(16) = 0, so k² = 64 and k = ±8. Since a positive value is required, k = 8. The option 64 is k², not k.

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