If $a_1, a_2, \ldots, a_n$ are in H.P., then the expression $a_1 a_2+a_2 a_3+\ldots+a_{n-1} a_n$ is equal to

If $a_1, a_2, \ldots, a_n$ are in H.P., then the expression $a_1 a_2+a_2 a_3+\ldots+a_{n-1} a_n$ is equal to
  1. $n\left(a_1-a_n\right)$
  2. $(n-1)\left(a_1-a_n\right)$
  3. $n a_1 a_n$
  4. $(n-1) a_1 a_n$

Asked in: JEE Main 2006

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