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Question

If a1,a2,a3,....,an are in A.P. where ai>0 for all i, show that 1a1+a2+1a2+a3+.....+1an1+an=(n1)a1+an

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Solution

L.H.S
1a1+a2+1a2+a3+......
=1(a1a2)(a1+a2)(a1a2)+1(a2a3)(a2+a3)(a2a3)+......
=a1a2a1a2+a2a3a2a3+......
=a2a1d+a3a2d+......
=ana1d×(an+a1an+a1)
=ana1(a1+an)d=(n1)a1+an

R.H.S
Hence, proved.

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