If b1,b2,b3,⋯,bnϵH.P. then b1b2+b2b3+b3b4+⋯,bn−1bn=
A
nb1bn
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B
(n+1)b1bn
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C
(n−1)b1bn
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D
None of these
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Solution
The correct option is C(n−1)b1bn Given that, b1,b2,b3,⋯,bnϵH.P. ⇒1b1,1b2,...1bnϵA.P. ∴d=b1−b2b1b2=b2−b3b2b3=...=bn−1−bnbn−1bn=b1−bn(n−1)b1bn ∴d=b1−bnb1b2+b2b3+...+bn−1bn ⇒b1−bn(n−1)b1bn=b1bn(1bn−1b1)b1b2+b2b3+...+bn−1bn Therefore, b1b2+b2b3+...+bn−1bn=(n−1)b1bn Ans: C