1.

If the second term of the expansion `[a^(1/(13))+a/(sqrt(a^(-1)))]^n`is `14 a^(5//2)`, then the value of `(^n C_3)/(^n C_2)`is.A. 4B. 3C. 12D. 6

Answer» Correct Answer - a
We have,
s`""^(n)C_(r) (root(13)(a))^(a-1) ((a)/(sqrt(a^(-1))))^(1) = 14 a^(5//2)`
`rArr na^((n+1)/(13)+(3)/(2)) = 14 a^(5//2) rArr n=14`
`therefore (""^(n)C_(3))/(""^(n)C_(2))=(n-2)/(3) = (14-2)/(3) = 4 [because (""^(n)C_(3))/(""^(n)C_(2))=(n-r+1)/(r)]` s


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