In the binomial (21/3+3−1/3)n if the ratio of the seventh term from the beginning of the expansion to the seventh term from its end is 1/6 then n is equal to
A
6
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B
9
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C
12
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D
15
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Solution
The correct option is B 9 From the above question we can conclude 6T7=Tn−7 Hence nC62n−63.3−2.6=nC636−n3.22 Hence (2.3)n−63.6=(2.3)2 Hence 6n−63=626=61 Comparing the indices, we get n−6=3 n=9.