Medium MCQ +4 / -1 PYQ · JEE Mains 2020

The following system of linear equations
7x + 6y – 2z = 0
3x + 4y + 2z = 0
x – 2y – 6z = 0, has

  1. A no solution
  2. B infinitely many solutions, (x, y, z) satisfying y = 2z
  3. C infinitely many solutions, (x, y, z) satisfying x = 2z Correct answer
  4. D only the trivial solution

Solution

Given <br>7x + 6y – 2z = 0 .......(1)<br> 3x + 4y + 2z = 0 ......(2)<br> x – 2y – 6z = 0 .......(3) <br><br>$\Delta$ = $$\left| {\matrix{ 7 &amp; 6 &amp; { - 2} \cr 3 &amp; 4 &amp; 2 \cr 1 &amp; { - 2} &amp; { - 6} \cr } } \right|$$ <br><br>= 7(–24 + 4) – 6(–18 – 2) – 2(–6 – 4) = 0 <br><br>$\therefore$ $\Delta$ = 0 <br><br>The system of equation has infinite non-trival solution. <br><br>Also adding equation (1) and 3$\times$(3), we get <br><br>10x = 20z <br><br>$\Rightarrow$ x = 2z

About this question

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

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