Let a_{1},a_{2},.,a_{n} be in A.P. If a_{5} = 2a_{7} and a_{11} = 18, then 12( \frac{1}{\sqrt{a_{10}} + \sqrt{a_{11}}} + \frac{1}{\sqrt{a_{11}} + \sqrt{a_{12}}} + .. + \frac{1}{\sqrt{a_{17}} + \sqrt{a_{18}}} ) is equal to : Sequence & Series (Mathematics) | DivineJEE