JEE Main & Advanced Mathematics Sequence & Series Question Bank Self Evaluation Test - Sequences and Series

  • question_answer
    The perimeter of a triangle whose sides are in A.P. is 21 cm and the product of lengths of the shortest side and the longest side exceeds the length of the other side by 6 cm. The longest side of the triangle is

    A) 1 cm

    B) 7 cm

    C) 13 cm

    D) None

    Correct Answer: C

    Solution :

    [c] Let the sides of the triangle be \[a-d,\,\,a,\,\,a+d,\] then Perimeter  \[=(a+d)+a+(a-d)=21\] \[\therefore \,\,\,a=7\] Again \[(a-d)\,\,(a+d)=a+6\] \[\Rightarrow \,\,\,{{a}^{2}}-{{d}^{2}}=a+6\Rightarrow 49-{{d}^{2}}=13\] \[\therefore \,\,\,\,d=\pm 6.\] Hence, the sides of the triangle are \[1\text{ }cm,\text{ }7\,cm,\text{ }13\,cm.\]


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