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

If the term independent of x in the expansion of x-kx210 is 405, then k=
  1. 3 only
  2. -3 only
  3. ±3
  4. 0

Solution

Tr+1=10cr·x10-r2-kr·x-2r

⇒10-r2-2r=0

⇒10-r=4r

⇒r=2

T3=10c2(-k)2=405

⇒45k2=405

⇒k2=9

⇒k=±3

 

Asked in: AP EAMCET 2020 (23 Sep Shift 1)

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