Binomial Theorem

Question
CBSEENMA11015583

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

  • 5/n −4

  • 6 /n −5

  • n -5 /6

  • n -4 /5

Solution

D.

n -4 /5

straight C presuperscript straight n subscript 4 space straight a to the power of straight n minus 4 end exponent space left parenthesis negative straight b right parenthesis to the power of 4 space plus straight C presuperscript straight n subscript 5 straight a to the power of straight n minus 5 end exponent space left parenthesis negative straight b right parenthesis to the power of 5 space equals space 0
rightwards double arrow space open parentheses straight a over straight b close parentheses space equals space fraction numerator straight n minus 5 plus 1 over denominator 5 end fraction

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