In each of these questions, two equations (I) and (II) are given. You have to…

2023

In each of these questions, two equations (I) and (II) are given. You have to solve both the equations and give the answer.

I. 3x2 − 14x + 15 = 0
II. 6y2 − 31y + 18 = 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 1 students.

Show answer & explanation

Correct answer: E

Concept: For two quadratic equations in x and y, first find all roots of each equation. A single inequality (x > y, x < y, x ≥ y or x ≤ y) can be declared the answer ONLY if that same relation holds for EVERY pairing of an x-root with a y-root. If different pairings give different directions, no single relation is valid and the answer is “no relation can be established”.

Application — Equation I: 3x2 − 14x + 15 = 0.

  1. Factorise: 3x2 − 14x + 15 = (3x − 5)(x − 3) = 0.

  2. So x = 5/3 ≈ 1.67 or x = 3.

Application — Equation II: 6y2 − 31y + 18 = 0.

  1. Factorise: 6y2 − 31y + 18 = (3y − 2)(2y − 9) = 0.

  2. So y = 2/3 ≈ 0.67 or y = 9/2 = 4.5.

Cross-check — compare every x with every y:

x

y

Relation

3

4.5

x < y

3

0.67

x > y

1.67

4.5

x < y

1.67

0.67

x > y

Some pairings give x < y and others give x > y, so the direction is not consistent. Therefore no single relation holds between x and y — the value “x = y or no relation can be established” is the result.

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