Let p and q be the roots of x^2 + p x + q = 0. Determine the correct values of (p, q) consistent with this definition.

Difficulty: Medium

Correct Answer: p = 1 and q = -2

Explanation:


Introduction / Context:
Here the symbolic coefficients p and q also equal the roots of their own quadratic. This creates equations among p and q via Vieta’s relations that must be satisfied simultaneously.


Given Data / Assumptions:

  • Equation: x^2 + px + q = 0.
  • Roots are p and q themselves.
  • Real values expected.


Concept / Approach:
For monic x^2 + px + q = 0 with roots r1 = p and r2 = q: sum r1 + r2 = −p and product r1*r2 = q (Vieta). This yields a system in p and q.


Step-by-Step Solution:

Sum: p + q = −p → q = −2p.Product: pq = q.Either q = 0 or p = 1.If q = 0 then q = −2p → p = 0 (gives (0, 0), not in options). If p = 1 then q = −2.Therefore (p, q) = (1, −2).


Verification / Alternative check:
With p = 1, q = −2, the quadratic x^2 + x − 2 = 0 has roots 1 and −2, matching p and q.


Why Other Options Are Wrong:
They violate either the sum or product condition; check Vieta’s relations to see inconsistencies.


Common Pitfalls:
Missing the special solution q = 0, p = 0 (not listed) or confusing coefficient p with root p without applying Vieta correctly.


Final Answer:
p = 1 and q = −2

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