JEE Main & Advanced Sample Paper JEE Main - Mock Test - 7

  • question_answer
    If \[{{a}^{2}},\text{ }{{b}^{2}},\text{ }{{c}^{2}}\]are in A.P. then \[\frac{1}{b+c},\frac{1}{c+a},\frac{1}{a+b}\] are in-

    A) A.P.                            

    B) GP.

    C) H.P.                            

    D) None of these

    Correct Answer: A

    Solution :

    \[\because \,\,{{a}^{2}},{{b}^{2}},{{c}^{2}}\]are in A.P.
    \[\therefore \,\,{{a}^{2}}+ab+bc+ca,\]\[{{b}^{2}}+bc+ca+ab,\] \[{{c}^{2}}+ca+ab+bc\] ..... are also in A.P. [adding \[ab+bc+ca\]]
    or \[\left( a+c \right)\,\left( a+b \right),\] \[\left( b+c \right)\left( a+b \right),\] \[\left( c+a \right)\left( b+c \right)\].. are also
    in A.P. \[\Rightarrow \,\,\,\frac{1}{b+c},\,\frac{1}{c+a},\,\frac{1}{a+b}\] are in A.P.
    [dividing by \[(a+b)\,(b+c)\,(c+a)\]]
     


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