10th Class Mathematics Triangles Question Bank MCQs - Triangles

  • question_answer
    In the given figure, if \[AB\left\| DC \right.,\] find the value of x.

    A) 5

    B) 7

    C) 6

    D) 4

    Correct Answer: B

    Solution :

    [b] Given \[AB||DC\]
    \[\therefore \,\,\,\angle ODC=\angle OBA\](Alternate interior angles)
    and   \[\angle OCD=\angle OAB\]
    (Alternate interior angles)
    \[\therefore \,\,\,\,\,\,\,\Delta DOC\tilde{\ }\Delta BOA\]
    (By AA similarity criterion)
                \[\therefore \,\,\,\,\,\frac{OD}{OB}=\frac{OC}{OA}\Rightarrow \frac{x-2}{x-1}=\frac{x+3}{x+5}\]
    \[\Rightarrow \,\,\,\,\,(x-2)\,(x+5)=(x+3)\,\,(x-1)\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,{{x}^{2}}+3x-10={{x}^{2}}+2x-3\,\,\Rightarrow \,\,x=7\]


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