Medium MCQ +4 / -1 PYQ · JEE Mains 2022

The ordered pair (a, b), for which the system of linear equations

3x $-$ 2y + z = b

5x $-$ 8y + 9z = 3

2x + y + az = $-$1

has no solution, is :

  1. A $\left( {3,{1 \over 3}} \right)$
  2. B $\left( { - 3,{1 \over 3}} \right)$
  3. C $\left( { - 3, - {1 \over 3}} \right)$ Correct answer
  4. D $\left( {3, - {1 \over 3}} \right)$

Solution

<p>$$\left| {\matrix{ 3 & { - 2} & 1 \cr 5 & { - 8} & 9 \cr 2 & 1 & a \cr } } \right| = 0 \Rightarrow - 14a - 42 = 0 \Rightarrow a = - 3$$</p> <p>Now 3 (equation (1)) $-$ (equation (2)) $-$ 2 (equation (3)) is</p> <p>$3(3x - 2y + z - b) - (5x - 8y + 9z - 3) - 2(2x + y + az + 1) = 0$</p> <p>$\Rightarrow - 3b + 3 - 2 = 0 \Rightarrow b = {1 \over 3}$</p> <p>So for no solution $a = - 3$ and $b \ne {1 \over 3}$

About this question

Subject: Mathematics · Chapter: Matrices and Determinants · Topic: Types of Matrices and Operations

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