If a1,a2,......a_1, a_2, ......a1,a2,...... are in A.P., then, 1a1+a2+1a2+a3+.......+1an+an+1\frac{1}{\sqrt{a_1} + \sqrt{a_2}} + \frac{1}{\sqrt{a_2} + \sqrt{a_3}} + ....... + \frac{1}{\sqrt{a_n} + \sqrt{a_{n + 1}}}a1+a21+a2+a31+.......+an+an+11 is equal to
na1+an+1\frac{n}{\sqrt{a_1} + \sqrt{a_{n + 1}}}a1+an+1n
n−1a1+an−1\frac{n - 1}{\sqrt{a_1} + \sqrt{a_{n - 1}}}a1+an−1n−1
n−1a1+an\frac{n - 1}{\sqrt{a_1} + \sqrt{a_n}}a1+ann−1
na1−an+1\frac{n}{\sqrt{a_1} - \sqrt{a_{n + 1}}}a1−an+1n
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