JEE Main & Advanced Mathematics Sequence & Series Question Bank Relation between AP., GP. and HP.

  • question_answer
    If A.M and G.M of x and y are in the ratio p : q, then x : y is [Kerala (Engg.) 2005]

    A) \[p-\sqrt{{{p}^{2}}+{{q}^{2}}}\]:\[p+\sqrt{{{p}^{2}}+{{q}^{2}}}\]

    B) \[p+\sqrt{{{p}^{2}}-{{q}^{2}}}\]:\[p-\sqrt{{{p}^{2}}-{{q}^{2}}}\]

    C) \[p:q\]

    D) \[p+\sqrt{{{p}^{2}}+{{q}^{2}}}\]:\[p-\sqrt{{{p}^{2}}+{{q}^{2}}}\]

    E) \[q+\sqrt{{{p}^{2}}-{{q}^{2}}}\]:\[q-\sqrt{{{p}^{2}}-{{q}^{2}}}\]

    Correct Answer: B

    Solution :

    \[\frac{\frac{x+y}{2}}{\sqrt{xy}}=\frac{p}{q}\] \[\frac{x+y}{2(\sqrt{xy})}=\frac{p}{q}\] ?..(i) \[\frac{{{x}^{2}}+{{y}^{2}}+2xy}{4xy}=\frac{{{p}^{2}}}{{{q}^{2}}}\] \[\frac{{{x}^{2}}+{{y}^{2}}+2xy-4xy}{4xy}=\frac{{{p}^{2}}-{{q}^{2}}}{{{q}^{2}}}\] \[\frac{{{(x-y)}^{2}}}{4xy}=\frac{{{p}^{2}}-{{q}^{2}}}{{{q}^{2}}}\] \[\frac{x-y}{2\sqrt{xy}}=\frac{\sqrt{{{p}^{2}}-{{q}^{2}}}}{q}\] ?..(ii) Equation (i) is divided by (ii), Then \[\frac{x+y}{x-y}=\frac{p}{\sqrt{{{p}^{2}}-{{q}^{2}}}}\]; \[\frac{x}{y}=\frac{p+\sqrt{{{p}^{2}}-{{q}^{2}}}}{p-\sqrt{{{p}^{2}}-{{q}^{2}}}}\].


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