In each of these questions, two equations (I) and (II) are given. Solve both…

2023

In each of these questions, two equations (I) and (II) are given. Solve both equations and choose the relation that holds between x and y.

I. 2x2 + 13x − 150 = 0

II. y2 − 17y + 66 = 0

  1. A.

    If x > y

  2. B.

    If x ≥ y

  3. C.

    If x < y

  4. D.

    If x ≤ y

  5. E.

    If x = y or no relation can be established between x and y

Attempted by 3 students.

Show answer & explanation

Correct answer: D

Concept

A quadratic ax² + bx + c = 0 has roots given by x = (−b ± √(b² − 4ac)) / (2a). To compare the two variables, find every root of each equation, then check the relation between each x-root and each y-root. A single answer (>, ≥, <, ≤, or no relation) holds only if it is consistent across ALL pairings.

Application

  1. Equation I: 2x2 + 13x − 150 = 0. Discriminant = 132 − 4(2)(−150) = 169 + 1200 = 1369 = 372.

  2. So x = (−13 ± 37) / 4, giving x = 24/4 = 6 and x = −50/4 = −12.5. Thus x ∈ {6, −12.5}.

  3. Equation II: y2 − 17y + 66 = 0 factors as (y − 6)(y − 11) = 0, so y ∈ {6, 11}.

  4. Compare each x with each y: 6 vs 6 gives x = y; 6 vs 11 gives x < y; −12.5 vs 6 gives x < y; −12.5 vs 11 gives x < y.

  5. Across all four pairings x is either equal to or less than y, and never greater. The consistent relation is therefore x ≤ y.

Cross-check

Plug the roots back: 2(6)² + 13(6) − 150 = 72 + 78 − 150 = 0 and (6)² − 17(6) + 66 = 36 − 102 + 66 = 0, both valid. The largest x (6) only ties the smaller y (6) and is below the larger y (11), confirming x can equal y but never exceed it, so x ≤ y.

Explore the full course: Niacl Ao It Specialist