The ratio of the coefficient of terms xn−rar and xran−r in the binomial expansion of (x+a)n will be
A
x:a
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B
n:r
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C
x:n
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D
none of these
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Solution
The correct option is D none of these (x+a)n=xn+Cn1xn−1a+...+Cnrxn−rar+...anSincethe(r+1)thtermisCnrxn−rar.RatioofcoefficentsisCnrCnn−rwhichisequalto1.Henceoption(D)