For which values of k does the equation x^2 + kx + 9 = 0 have exactly one real solution?
Answer and explanation
Correct answer: D. k = 6 or k = -6
- Step 1: One real solution means the discriminant is zero: k^2 - 4(1)(9) = 0. Step 2. k^2 = 36, so k = 6 or k = -6. Answer: k = 6 or k = -6. Why not the others: k = 3 or -3 takes the square root of 9 instead of 36, k = 9 only ignores the discriminant and the negative root, and k = 18 or -18 uses 2 x 9 instead of the square root of 36.
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