1.

If A and B are the coefficients of `x^n` in the expansion `(1 + x)^(2n)` and `(1 + x)^(2n-1)` respectively, thenA. A= BB. 2A = BC. A = 2BD. none of these

Answer» Correct Answer - c
We have,
A = Coefficient of `x^(n)` in `( 1 + x)^(2n)`
`rArr A = ""^(2n)C_(n)`
`rArr A = (2n)/(n) ""^(2n-1)C_(n-1) = 2 ""^(2n-1)C_(n-1) [because ""^(n)C_(r) = (n)/(r) ""^(n-1)C_(n-1) ]` and
B = Coefficient of `x^(n) ` in `(1 + x)^(2n-1)`
`rArr B= ""^(2n -1)C_(n) = ""^(2n-1) C_(n-1) [because ""^(n)C_(r) = ""^(n)C_(n-r)]`
Clearly, A = 2B.


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