10th Class Mathematics Triangles Question Bank MCQs - Triangles

  • question_answer
     
    In the given figure, \[\angle ABC=90{}^\circ \]and \[BD\bot AC\]. If BD = 8 cm and AD = 4 cm, then the value of CD is

    A) 8 cm

    B) 12cm

    C) 14cm

    D) 16cm

    Correct Answer: D

    Solution :

    Given, BD = 8 cm and AD = 4 cm
    In \[\Delta ADB\] and      \[\Delta BDC\],
    \[\angle BDA=\angle CDB\]         [each \[90{}^\circ\]]
    \[\angle DBA=\angle DCB\]         [each \[\left( 90{}^\circ -\angle A \right)\]]
    \[\therefore \Delta ADB\tilde{\ }\Delta BDC\]
                             [by AA similarity criterion]
    \[\Rightarrow \,\,\,\frac{BD}{CD}=\frac{AD}{BD}\]
                            (since, corresponding sides of similar triangles are proportional]
    \[\Rightarrow \,\,\,\,CD=\frac{B{{D}^{2}}}{AD}\]
    \[\therefore \,\,\,CD=\frac{{{8}^{2}}}{4}=\frac{64}{4}=16\,\,cm\]
     


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