JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Determinats

  • question_answer
    If the system of linear equations \[x+2ay+az=0;\] \[x+3by+bz=0;\] \[x+4cy+cz=0\] has a non - zero solution, then a, b, c.

    A) Satisfy  \[a+2b+3c=0\]

    B) Are in A.P

    C) Are in G.P

    D) Are in H.P.

    Correct Answer: D

    Solution :

    [d] For homogeneous system of equations to have non zero solution, \[\Delta =0\] \[\left| \begin{matrix}    1 & 2a & a  \\    1 & 3b & b  \\    1 & ac & c  \\ \end{matrix} \right|=0[\therefore {{C}_{2}}\to {{C}_{2}}-2{{C}_{3}}]\] \[\left| \begin{matrix}    1 & 0 & a  \\    1 & b & b  \\    1 & 2c & c  \\ \end{matrix} \right|=0\,[{{R}_{3}}\to {{R}_{3}}-{{R}_{2}},\,\,{{R}_{2}}\to {{R}_{2}}-{{R}_{1}}]\] On simplification, \[\frac{2}{b}=\frac{1}{a}+\frac{1}{c}\] \[\therefore \] a, b, c are in Harmonic Progression.


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