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Home  >>  JEEMAIN and AIPMT  >>  Mathematics  >>  Class11  >>  Sequence and Series
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If $a_{1},a_{2},...a_{n}$ are in HP. , Then $\;a_{1}a_{2}+a_{2}a_{3}+.....+a_{n}\;a_{n-1}$ is equal to


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Answer : $(c)\;(n-1)a_{1}a_{n}$
Explanation : $a_{1}\;,a_{2}\;....\;a_{n}\;$ are in HP
$\frac{1}{a_{1}}\;,\frac{1}{a_{2}}\;,....\;\frac{1}{a_{n}}\;$ are in AP
answered Jan 20, 2014 by yamini.v

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