Compare roots from two quadratics (check all combinations): I) 24x^2 + 38x + 15 = 0 II) 12y^2 + 28y + 15 = 0 Decide the correct relationship that always holds between any root x of I and any root y of II.

Difficulty: Medium

Correct Answer: x ≥ y

Explanation:


Introduction / Context:
When comparing two quadratics, each with two real roots, we must confirm that a proposed inequality holds across all four pairings (each x with each y). A single counterexample invalidates a universal statement like x ≥ y. Here we solve both quadratics and compare the root sets carefully.


Given Data / Assumptions:

  • I) 24x^2 + 38x + 15 = 0
  • II) 12y^2 + 28y + 15 = 0
  • All comparisons are between any root x of I and any root y of II.


Concept / Approach:
Compute exact roots via discriminants. Then order the roots numerically and check whether the smallest x is still ≥ the largest y (for x ≥ y), or similar tests for other relations. If equality can occur for some pairing and strict inequality for others, then ≥ (not >) may be the correct consistent relation.


Step-by-Step Solution:

I) D = 38^2 − 4*24*15 = 1444 − 1440 = 4 ⇒ √D = 2x = (−38 ± 2)/(48) ⇒ x ∈ {−36/48, −40/48} = {−3/4, −5/6}II) D = 28^2 − 4*12*15 = 784 − 720 = 64 ⇒ √D = 8y = (−28 ± 8)/(24) ⇒ y ∈ {−20/24, −36/24} = {−5/6, −3/2}Order: x-roots = {−0.75, −0.833…}; y-roots = {−0.833…, −1.5}Check: smallest x = −0.833… ≥ largest y = −0.833… (true, equality), and any x ≥ any y (true)


Verification / Alternative check:
Test all pairings: (−0.75 ≥ −0.833…), (−0.75 ≥ −1.5), (−0.833… ≥ −0.833…), (−0.833… ≥ −1.5). All hold; at least one pairing yields equality, so x ≥ y is the strongest always-true statement.


Why Other Options Are Wrong:

  • x > y: Fails at equality case (−5/6 vs −5/6).
  • x ≤ y or x < y: Contradicted by −0.75 ≥ −0.833…
  • Relationship cannot be determined: We just established a universal relation.


Common Pitfalls:
Overlooking equal roots across equations or assuming strict inequality without testing equality. Always check extremes to decide between > and ≥.


Final Answer:
x ≥ y

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