10th Class Mathematics Triangles Question Bank MCQs - Triangles

  • question_answer
    In the adjoining figure, \[DE\left\| BC \right.\]. The value of x is:

    A) 4

    B) 6

    C) 8

    D) 10

    Correct Answer: C

    Solution :

    [c] In \[\Delta ABC,\] \[DE||BC\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{AD}{DB}=\frac{AE}{EC}\]       (By Thales theorem)
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{2x-1}{x-3}=\frac{2x+5}{x-1}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,(2x-1)\,\,(x-1)=(2x+5)\,(x-3)\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,2{{x}^{2}}-2x-x+1=2{{x}^{2}}+5x-6x-15\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,2x=16\,\,\,\,\,\,\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\,\,\,x=8\]


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