Construct a quadratic from sum and product of roots: Form the quadratic equation whose roots have sum 6 and product −16.
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Ax^2 − 6x − 16 = 0
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Bx^2 + 6x − 16 = 0
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Cx^2 − √3x − 16 = 0
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DNone of these
Answer
Correct Answer: x^2 − 6x − 16 = 0
Explanation
Introduction / Context:Given the sum (S) and product (P) of roots, the monic quadratic is x^2 − Sx + P = 0. This is a direct application of Vieta’s relations and avoids computing the individual roots.Given Data / Assumptions:
- Sum S = 6.
- Product P = −16.
Concept / Approach:Write x^2 − Sx + P = 0. Substitute S and P as provided, ensuring the signs are placed correctly (note that P is negative here).
Step-by-Step Solution:
General form: x^2 − Sx + P = 0.With S = 6 and P = −16: x^2 − 6x − 16 = 0.Verification / Alternative check:If roots are r1 and r2, then r1 + r2 = 6 and r1*r2 = −16. Expanding (x − r1)(x − r2) gives x^2 − (r1 + r2)x + r1r2 = x^2 − 6x − 16, as required.
Why Other Options Are Wrong:
- x^2 + 6x − 16 = 0: Has sum −6.
- x^2 − √3x − 16 = 0: Introduces an irrelevant irrational coefficient.
- None of these: Incorrect because x^2 − 6x − 16 = 0 matches exactly.
Common Pitfalls:Mixing the sign of P or writing x^2 − Sx − P by mistake. Always align with x^2 − Sx + P.
Final Answer:
x^2 − 6x − 16 = 0