JEE Main & Advanced Mathematics Straight Line Question Bank Self Evaluation Test - Straight Lines & Pair Striaght Lines

  • question_answer
    If 2p is the length of perpendicular from the origin to the lines \[\frac{x}{a}+\frac{y}{b}=1\], then \[{{a}^{2}},8{{p}^{2}},{{b}^{2}}\] are in

    A) A.P

    B) GP.

    C) H.P.

    D) None of these

    Correct Answer: C

    Solution :

    [c] We have \[2p\left| \frac{0+0-1}{\sqrt{\frac{1}{{{a}^{2}}}+\frac{1}{{{b}^{2}}}}} \right|\Rightarrow \frac{1}{{{a}^{2}}}+\frac{1}{{{b}^{2}}}=\frac{1}{4{{p}^{2}}}\] \[\frac{1}{{{a}^{2}}}+\frac{1}{{{b}^{2}}}=\frac{2}{8{{p}^{2}}}\Rightarrow \frac{1}{{{a}^{2}}},\frac{1}{8{{p}^{2}}},\frac{1}{{{b}^{2}}}\] are in A.P. \[\Rightarrow {{a}^{2}},8{{p}^{2}},{{b}^{2}}\] are in H.P.


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