10th Class Mathematics Triangles Question Bank MCQs - Triangles

  • question_answer
    In figure, \[LM\left\| AB \right.\]. If \[AL=x-3,\]\[AC=2x,\]\[BM=x-2\]and \[\text{BC}=\text{2x}+\text{3},\]find the value of x.                 

    A) 2

    B) \[9.5\]

    C) 9

    D) \[8.5\]

    Correct Answer: C

    Solution :

    [c] In \[\Delta ABC,\] \[LM||AB\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\frac{AL}{LC}=\frac{BM}{MC}\]         (By Thales theorem)
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{AL}{AC-AL}=\frac{BM}{BC-BM}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{x-3}{2x-(x-3)}=\frac{x-2}{(2x+3)-(x-2)}\Rightarrow \frac{x-3}{x+3}=\frac{x-2}{x+5}\]\[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(x-3)\,\,(x+5)=(x-2)\,(x+3)\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{x}^{2}}+2x-15={{x}^{2}}+x-6\,\,\,\,\,\,\,\,\,\Rightarrow \,\,x=9\]


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