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

If the system of linear equations
2x + 2ay + az = 0
2x + 3by + bz = 0
2x + 4cy + cz = 0,
where a, b, c $\in$ R are non-zero distinct; has a non-zero solution, then:

  1. A ${1 \over a},{1 \over b},{1 \over c}$ are in A.P. Correct answer
  2. B a + b + c = 0
  3. C a, b, c are in G.P.
  4. D a,b,c are in A.P.

Solution

For non-zero solution <br><br>$$\left| {\matrix{ 2 &amp; {2a} &amp; a \cr 2 &amp; {3b} &amp; b \cr 2 &amp; {4c} &amp; c \cr } } \right| = 0$$ <br><br>$\Rightarrow$ $$\left| {\matrix{ 1 &amp; {2a} &amp; a \cr 0 &amp; {3b - 2a} &amp; {b - a} \cr 0 &amp; {4c - 2a} &amp; {c - a} \cr } } \right| = 0$$ <br><br>$\Rightarrow$ (3b – 2a) (c –a) – (b – a) (4c – 2a) = 0 <br><br>$\Rightarrow$ 2ac = bc + ab <br><br>$\Rightarrow$ ${2 \over b} = {1 \over a} + {1 \over c}$ <br><br>$\therefore$ ${1 \over a},{1 \over b},{1 \over c}$ are in A.P.

About this question

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

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