10th Class Mathematics Triangles Question Bank Triangles

  • question_answer
    In the given figure, \[AD\bot BC,\] \[BE\bot AC,\]\[CF\bot AB,\] then \[A{{F}^{2}}+B{{D}^{2}}+C{{E}^{2}}=\]

    A)  \[O{{A}^{2}}+O{{B}^{2}}+O{{C}^{2}}\] 

    B)  \[O{{D}^{2}}+O{{E}^{2}}+O{{F}^{2}}\]

    C)  \[A{{B}^{2}}+B{{C}^{2}}+A{{C}^{2}}\]

    D)  \[A{{E}^{2}}+B{{F}^{2}}+C{{D}^{2}}\]

    Correct Answer: D

    Solution :

    In \[\Delta ODB\]and \[\Delta ODC,\] using Pythagoras theorem. \[O{{B}^{2}}=O{{D}^{2}}+B{{D}^{2}}\]and \[O{{C}^{2}}-O{{D}^{2}}+C{{D}^{2}}\] \[\therefore \]    \[O{{B}^{2}}-O{{C}^{2}}=B{{D}^{2}}-C{{D}^{2}}\]            ?.(i) Similarity, we have \[O{{C}^{2}}-O{{A}^{2}}=C{{E}^{2}}-A{{E}^{2}}\]                 ?..(ii) And  \[O{{A}^{2}}-O{{B}^{2}}=C{{E}^{2}}-A{{E}^{2}}\]         ?..(iii) Adding (i), (ii) and (iii), we get \[B{{D}^{2}}+C{{E}^{2}}+A{{F}^{2}}-C{{D}^{2}}-A{{E}^{2}}-B{{F}^{2}}=0\] \[\Rightarrow \] \[B{{D}^{2}}+C{{E}^{2}}+A{{F}^{2}}=C{{D}^{2}}+A{{E}^{2}}+B{{F}^{2}}\]


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