10th Class Mathematics Triangles Question Bank Triangles

  • question_answer
    In rhombus ABCD \[A{{B}^{2}}+B{{C}^{2}}+C{{D}^{2}}+D{{A}^{2}}=\]                        

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

    B)  \[O{{B}^{2}}+O{{C}^{2}}\]

    C)                     \[O{{C}^{2}}+O{{D}^{2}}\]

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

    Correct Answer: D

    Solution :

    Let the length of sides of rhombus be x, length of OC be \[{{x}_{1}}\] and length of OD be \[{{y}_{1}}\]Then, \[A{{B}^{2}}+B{{C}^{2}}+C{{D}^{2}}+D{{A}^{2}}=4{{x}^{2}}\] Since, AC and DB bisect each other at O. \[\therefore \]  \[AC=2{{x}_{1}}\] and \[BD=2{{y}_{1}}\] In  \[\Delta AOD,\text{ }\Delta DOC,\text{ }\Delta AOB,\text{ }\Delta BOC\] \[4\left[ x_{1}^{2}+y_{1}^{2} \right]=4{{x}^{2}}\] \[\Rightarrow \]  \[A{{C}^{2}}+B{{D}^{2}}=A{{B}^{2}}+B{{C}^{2}}+C{{D}^{2}}+A{{D}^{2}}\]


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