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AP EAMCET202023 Sep 2020Morning ShiftMathematicsBinomial TheoremActual

If the term independent of x in the expansion of x - k x 2 10 is 405 , then k =

Options

  1. A3 only
  2. B- 3 only
  3. C± 3
  4. D0

Correct answer

C. ± 3

Step-by-step solution

T r + 1 = 10 c r · x 10 - r 2 - k r · x - 2 r ⇒ 10 - r 2 - 2 r = 0 ⇒ 10 - r = 4 r ⇒ r = 2 T 3 = 10 c 2 ( - k ) 2 = 405 ⇒ 45 k 2 = 405 ⇒ k 2 = 9 ⇒ k = ± 3

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