alleryFor what k does x^2 + kx + 9 = 0 have equal roots?
Ak = plus or minus 6
Bk = plus or minus 3 by alternative method
Ck = plus or minus 9 by alternative method
Dk = plus or minus 12 by alternative method
Answer & Solution
Correct answer: A. k = plus or minus 6
1. Equal roots require D = 0.
2. D = k^2 - 4 * 1 * 9 = k^2 - 36.
3. k^2 = 36 gives k = plus or minus 6.
4. Hence k = plus or minus 6.
_Source: Selina Concise Mathematics Class 10, Ch 5 Quadratic Equations (Mistral OCR'd PDF), section on nature of roots_
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