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JEE Mains · Maths · STD 11 - 7. binomial theoram

The coefficient of \(x ^{101}\) in the expression \((5+x)^{500}+x(5+x)^{499}+x^{2}(5+x)^{498}+\ldots . x^{500}\) \(x>0\), is

  1. A \({ }^{501} C _{101}(5)^{399}\)
  2. B \({ }^{501} C _{101}(5)^{400}\)
  3. C \({ }^{501} C _{100}(5)^{400}\)
  4. D \({ }^{500} C _{101}(5)^{399}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \({ }^{501} C _{101}(5)^{399}\)

Step-by-step Solution

Detailed explanation

\((5+x)^{500}+x(5+x)^{499}+x^{2}(5+x)^{498}+\ldots+x^{500}\) \(=\frac{(5+x)^{501}-x^{501}}{(5+x)-x}=\frac{(5+x)^{501}-x^{501}}{5}\) \(\Rightarrow\) coefficient \(x ^{101}\) in given expression \(=\frac{{ }^{501} C _{101} 5^{400}}{5}={ }^{501} C _{101} 5^{399}\)