JEE Main & Advanced Mathematics Straight Line Question Bank Concurrency of three lines

  • question_answer
    If the given lines \[y={{m}_{1}}x+{{c}_{1}},y={{m}_{2}}x+{{c}_{2}}\] and \[y={{m}_{3}}x+{{c}_{3}}\] be concurrent, then

    A)            \[{{m}_{1}}({{c}_{2}}-{{c}_{3}})+{{m}_{2}}({{c}_{3}}-{{c}_{1}})+{{m}_{3}}({{c}_{1}}-{{c}_{2}})=0\]

    B)            \[{{m}_{1}}({{c}_{2}}-{{c}_{1}})+{{m}_{2}}({{c}_{3}}-{{c}_{2}})+{{m}_{3}}({{c}_{1}}-{{c}_{3}})=0\]

    C)            \[{{c}_{1}}({{m}_{2}}-{{m}_{3}})+{{c}_{2}}({{m}_{3}}-{{m}_{1}})+{{c}_{3}}({{m}_{1}}-{{m}_{2}})=0\]     

    D)            None of these

    Correct Answer: A

    Solution :

               \[\left| \begin{matrix}    {{m}_{1}} & -1 & {{c}_{1}}  \\    {{m}_{2}} & -1 & {{c}_{2}}  \\    {{m}_{3}} & -1 & {{c}_{3}}  \\ \end{matrix} \right|=0\]                    Þ \[{{m}_{1}}({{c}_{2}}-{{c}_{3}})+{{m}_{2}}({{c}_{3}}-{{c}_{1}})+{{m}_{3}}({{c}_{1}}-{{c}_{2}})=0\].               Note: Students should remember this question as a formula.


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