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JEE Main2007MathematicsBinomial TheoremActual

In the binomial expansion of (a-b)^n, n 5 , the sum of 5^ th and 6^ th terms is zero, then a b equals

Options

  1. A5 n-4
  2. B6 n-5
  3. Cn-5 6
  4. Dn-4 5

Correct answer

D. n-4 5

Step-by-step solution

^n C₄ a^ n-4 (-b)^4+ ^n C₅ a^ n-5 (-b)^5=0 ( a b )= n-5+1 5 .

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