Difficulty: Medium
Correct Answer: 12x^2 - 19x + 4 = 0
Explanation:
Introduction / Context:
This tests the reciprocal-root transformation. Given a quadratic with roots α and β, we are to construct the equation for roots 1/α and 1/β without explicitly finding α and β.
Given Data / Assumptions:
Concept / Approach:
For ax^2 + bx + c = 0, sum α + β = −b/a and product αβ = c/a. Then for reciprocals: (1/α) + (1/β) = (α + β)/(αβ) and (1/α)(1/β) = 1/(αβ). The monic form is x^2 − [(α + β)/(αβ)]x + [1/(αβ)] = 0, which can be scaled to clear denominators.
Step-by-Step Solution:
Verification / Alternative check:
Direct transformation rule: cx^2 + bx + a = 0 for reciprocals gives 12x^2 − 19x + 4 = 0, consistent.
Why Other Options Are Wrong:
Signs or placements of coefficients are incorrect; only option with pattern c, b, a works.
Common Pitfalls:
Forgetting to divide by product αβ when summing reciprocals; not clearing denominators cleanly.
Final Answer:
12x^2 − 19x + 4 = 0
Discussion & Comments